Nearly halfway through the year, 2015 is proving to be a big one for mergers and acquisitions (M&A). With the Federal Reserve Bank indicating that it may raise its target interest rates later this year, the prolonged low-interest rate environment and the cheap money brought with it, may be ending soon. As a result, corporations looking to grow through acquisition are taking a good look at takeover candidates and making these deals happen before it's too late.

Here is a look at the top ten biggest M&A deals (in dollar amount) so far for 2015, dominated mainly by deals in the pharmaceutical / healthcare and technology sectors. (For more, see: The Basics of Mergers & Acquisitions.)

10. CVS to acquire Omnicare  ($12.7 billion)

Pharmacy chain CVS Health (CVS) announced this year a deal to acquire Omnicare (OCR), a leading provider of pharmacy services to elder care and long term care facilities for nearly $12.7 billion, including $2.3 billion in debt. This deal will allow CVS to better access new distribution channels to older consumers. Senior citizens are a growing demographic in the healthcare sector. (See also: How Mergers and Acquisitions Can Effect a Company.)

9. OptumRx to acquire Catamaran Corp. ($12.8 billion)

In another healthcare deal, OptimRX, which is United Healthcare's (UNH) pharmacy service, agreed to combine with Catamaran Corp. (CTRX), formerly known as SXC Health Solutions. Catamaran is a leading provider of pharmacy benefit management (PBM) services. The combined company will have better scope and scale in servicing customers' pharmaceutical needs.

8. Williams to acquire Williams Partners ($13.8 billion)

Oil services company Williams (WMB) has agreed to acquire all outstanding common units of Williams Partners (WPZ) in a deal valued at $13.8 billion. Williams Partners, formerly Access Midstream Partners, L.P. owns, operates, develops and acquires natural gas, natural gas liquids (NGL). and oil gathering systems. The deal is expected to benefit shareholders of both companies during a short-term period of low oil prices . (For more, see: Analyzing an Acquisition Announcement.)

7. Danaher to acquire Pall Corp. ($13.8 billion)

Industrial equipment company Danaher (DHR) is buying Pall Corp. (PLL), a leading maker of filter and filtration technologies for $13.8 billion. Danaher's President & CEO, Thomas P. Joyce, Jr., said, "Pall is a highly attractive business, with approximately 75% recurring revenues, mid-single digit organic growth and a solid margin profile."

6. Valeant Pharmaceuticals to acquire Salix Pharmaceuticals ($14.5 billion)

Valeant Pharmaceuticals International (VRX), formerly Biovail Corporation, is a specialty pharmaceutical company that develops, manufactures and markets a range of specialized pharmaceutical products. They announced that they will buy Salix Pharma (SLXP), also a specialty drug manufacturer focusing on gastrointestinal diseases, for $14.5 billion. J. Michael Pearson, Valeant's chairman and Chief Executive Officer said of the deal: "The growing GI market has attractive fundamentals, and Salix has a portfolio of terrific products that are outpacing the market in terms of volume growth and a promising near-term pipeline of innovative products."

5. Intel to acquire Altera ($16.7 billion)

Leading microchip maker Intel (INTC) has announced it intends to buy Altera (ALTR) in a deal worth $16.7 billion. The deal will allow Intel to expand its product line to include Altera's unique range of products, including programmable logic devices (PLDs), highly integrated power devices, pre-defined design building blocks, and development software. PLDs consist of field-programmable gate arrays (FPGAs), which are microchips that the company's customers program to perform specific desired logic and processing functions in their electronic systems. (See also: How to Profit from Mergers & Acquisitions Through Arbitrage.)

4. Pfizer to acquire Hospira ($17 billion)

Pharmaceutical giant Pfizer (PFE) is buying Hospira (HSP) in a deal worth approximately $17 billion, and giving Pfizer access to Hospira's portfolio of generic acute-care and oncology injectables, biosimilars, and integrated infusion therapy and medication management products. Ian Read, Pfizer's Chairman and Chief Executive Officer, says, “In addition, Hospira’s business aligns well with our new commercial structure and is an excellent strategic fit for our Global Established Pharmaceutical business, which will benefit from a significantly enhanced product portfolio in growing markets."

3. AbbVie to acquire Pharmacyclics ($21 billion)

Chicago-based pharmaceutical company AbbVie (ABBV) will acquire Pharmacyclics (PCYC) and its flagship asset Imbruvica, an effective treatment for blood-based diseases. The acquisition accelerates AbbVie's clinical and commercial presence in cancer treatment and establishing a leading position in hematological oncology, a rapidly growing market, worth around $24 billion. The deal is worth approximately $21 billion. (See also: Mergers & Acquisitions: Understanding Takeovers.)

2. Avago Tech to acquire Broadcom ($31 billion)

Specialized semiconductor manufacturer Avago Tech (AVGO) is buying its rival Broadcom (BRCM) in a $31 billion deal, creating a combined company that will have the most diversified communications platform in the semiconductor industry, with combined yearly revenues of $15 billion. This consolidation comes at a time when mobile technology and communications are dominant sectors in the tech economy.

1. Charter Communications to acquire Time Warner Cable ($78.7 billion)

Telecommunications giant Charter Communications (CHTR) is going to merge with Time Warner Cable (TWC) for $78.7 billion, creating one of the largest cable television and broadband internet providers in existence. This deal is not only the largest in dollar size for 2015, but also the biggest in recent history. The deal is subject to the approval by shareholders of both companies, and will also be scrutinized by regulators to ensure that the combined company does not result in a monopoly that will harm customers or stifle competition. Interestingly, Time Warner Cable was created from its former parent Time Warner, which was involved in the largest M&A deal of all time: the combination of AOL and Time Warner, which closed for $186.2 billion in the year 2000, and which has been largely regarded as one of the worst corporate deals in history. (See also: Biggest M&A Disasters.)

The Bottom Line

It is largely considered a good sign for the economy and economic growth when mergers and acquisitions activity picks up, and so far 2015 has been the most active year since the Great Recession. This year's deals have been dominated by takeovers in the technology and healthcare sectors, and if the trend continues, this year is on track to break records.

With the central bank indicating that the era of historically low interest rates is coming to end sooner rather than later, companies are actively seeking to take advantage of cheap money before it's too late. Whether or not this increase in M&A activity is a result of economic fundamentals or just a rush to the gates before interest rates begin rising is yet to be seen.