The Wheel of Time series is not the same as most of the other series mentioned here. It is a serial - a single story told in 14 volumes - rather than a series of stand-alone stories featuring the same characters.
I can't off-hand think of any other serial of comparable length, although there are plenty of much longer series. It's kind of traditional to run into the tens of books about a single detective in crime fiction. I admit to being slightly intimidated when I looked at the Nero Wolfe wikipedia page.
Epic fantasy tends to run to trilogies, sometimes fours or fives. Longer sequences (such as Recluce) are usually not serials. Song of Ice and Fire is unfinished at 5, so far.