If not for major economic issues like the collapse in oil prices, the pullback in the Chinese economy and the liftoff of interest rates, the continued rise of exchange-traded funds would compete for the top financial story in 2015.

Despite questions surrounding the August 24 ETF "flash crash," when the prices of some ETFs declined well below their net asset value at the beginning of the day’s trading, investors continued to flock to these products. In response, a flood of new ETFs were introduced throughout the year—but most of the top 15 ETFs by trading volume are tried-and-true favorites of investors, according to a list pubished by New York-based global ETF research firm XTF.

In fact, the top three ETFs were rather vanilla index funds.

XTF ranked funds by their average daily trading volume in dollars. For comparison, we've included the average daily volume by shares as reported by Morningstar on Wednesday.

15. VelocityShares Daily Inverse VIX Short Term ETN – XIV

Average daily volume: $869 million

The VelocityShares Daily Inverse VIX Short Term ETN, which tracks the inverse of VXX, was also popular among traders during the volatility in the second half of 2015. 

The fund experienced an average volume of 22.9 million shares per day.

14. Market Vectors Trust Gold Miners – GDX  

Average Daily Volume: $874 million

As it lost 75 percent of its value in the third quarter amid sagging commodity prices, the Market Vectors Trust Gold Miners ETF was traded heavily by institutional investors and bargain hunters alike, with an average daily volume of 50.9 shares traded.

13. Financial Select Sector SPDR Fund – XLF

Average Daily Volume: $966 million

Perhaps investors trying to play the much-anticipated Fed interest rate hike announcement chose XLF as their vehicle—the fund’s 1.8 percent dividend yield over the past 12 months may also be an attraction. The low-cost ETF traded briskly, with an average daily volume of 36 million shares a day.