Will merger mania continue in 2016?

You'd probably expect mergers-and-acquisitions professionals to be giddy with optimism as we prepare to ring in a New Year. After all, 2015 has been a record-setter in merger land, even as the U.S. stock market has essentially stood still.

The list of blockbuster deals this year reads like a who's who of corporate brands across industries: Pfizer-Allergan, Dow Chemical-DuPont, Anheuser Bush InBev-SABMiller, Dell-EMC, Anthem-Cigna, AT&T-Direct TV, Marriott-Starwood, Walgreen's-Rite Aid.

Handshake M&A mergers
Saklakova | Getty Images

Added together, the value of 2015's M&A transactions is well over a record $4.5 trillion and could hit $5 trillion by the time the ball drops in Times Square. And the volume of transactions, is close to breaking the mark of 40,000 deals worldwide, as measured by Thomson Reuters.

But in spite of all the year's deal-making, investment bankers are relatively sober in their outlook as they anticipate popping the cork on 2016. That's because early indications are that 2015 will be the peak, with a slight decline coming next year in merger and acquisition volume.

A brand new Intralinks survey of 680 global M&A professionals dealmakers finds:

• Just under half — 48 percent — in North America, say they are optimistic about the current deal environment, a low figure considering this year's record. Globally, exactly half of the investment bankers are optimistic.

• Only 45 percent of North American investment bankers expect to participate in more deals during the first half of 2016 than during the prior 6 months. Worldwide, 49 percent of M&A pros anticipate a role in more deals during the coming 6 months.

• Investment bankers expect deal valuation will be the most difficult part of the M&A process, a reflection of the strong prices currently being paid to make acquisitions, with 45 percent anticipating valuations will remain flat through the end of the first half of 2016.

These are informed opinions, not merely guesses, because investment bankers, after all, work within the deal pipeline. For them, today's labor can be tomorrow's deal. The latest measure of their early stage merger activity – corporate due diligence – a reliable indicator of deals six months in the future, revealed a decline of 3 percent in North America during the third quarter, the first drop in more than two years as tracked by Intralinks' Deal Flow Predictor. Meanwhile, on a global basis, early stage merger and acquisition activity rose at the slowest quarterly pace in 2-1/2 years.

Even on the heels of a record year, there are reasons for concern. Commodity prices are experiencing an historic plunge. Equity markets have been showing weakness, even as deal valuations have climbed, an unhealthy divergence. Though the Federal Reserve has finally made its first move to raise short-term interest rates, the policy outlook remains uncertain, with some investors worried Fed governors may commit to their "dot plot" of higher rates before the economy can fully absorb tighter monetary policy. Many emerging market economies appear particularly shaky, and, of course, growth has been slowing in China. Deal makers responding to our survey expressed concern that emerging market problems and sluggishness in China could drag the global economy into a slowdown that would hurt their business.

To be sure, the old Wall Street proverb, "Bull markets climb walls of worry," can apply as easily to the deal market as it can to market for equities. We anticipate a continued robust market for mergers and acquisitions in the first quarter of 2016, with an increase in the volume of deals, compared to 2015's first quarter. But, as the year progresses, there very well may be a slowdown that will leave 2015 as the all-time record year for mergers and acquisitions.

Commentary by Matt Porzio, vice president of strategy for Intralinks, which offers secure online file-sharing systems for businesses. Follow him at @MattPorzio.