Various factors accounted for such explosive growth; among them, the Deal Book said, were accelerating activity across all buyer categories, the reemergence of private equity and banks as acquirers and the aging demographics of RIA owners.

But the company believes there's more volume to come.

"The continued surge in RIA M&A activity over the last two years is a natural phase of consolidation that most hyperfragmented industries experience as they mature," David DeVoe, managing partner at DeVoe & Company, said in a statement. DeVoe added, "We expect this momentum to continue and potentially accelerate over the next five to seven years."

While 2015 was a standout year for number of deals, it was also notable for additional reasons—such as the fact that firms continued to buy and sell despite a market that was turbulent at best. Past experience indicates that significant stock market declines and sustained market volatility can weigh on M&A activity among RIAs, keeping advisors preoccupied with soothing clients and monitoring the market rather than arriving at terms with potential buyers or sellers.

In addition, RIA valuations can suffer from extreme volatility or market declines, because of higher risk and/or lower revenue from client assets.

That can make advisors hesitant to sell at lower prices. But that hesitation was not in evidence during 2015.

It wasn't just deals, but big deals, too.

While M&A activity was up pretty much across the spectrum, what the report referred to as "megadeals"—transactions involving sellers with more than $5 billion in assets under management—figured prominently. During 2015, 13 firms managing AUM of $5 billion or more topped the sales list. In 2014, only two such firms sold to a third party, and in 2013 just three such megadeals took place.