games are not about 15 minutes. (i had the alpha, and have the beta)
but yes games are generally faster than Aok. The length of the game really depends on how close in skill you are with your opponent. The fighting generally starts just before 10 min. (you get to the seconed age at 5-6:30min) 1vs1 games can be over in 15 min, but then you have to be playing against either much much better than you, or vise versa.
If you happen to be of equal skill games seemed to last around 45 min, and go well into mythic age. But i would say the average length of a game is 30 min.