15 minutes in Cata heroics would be quite hard except for the really short heroics. 15 minutes was pretty typical in Wrath though, and even fairly long for some of them! I remember doing a 7 minute run of Gun'drak once from entering to killing the last boss, so some of those could be done really fast. My runs now usually take from 25-60 minutes depending on how many guildies I have with me, and what the overall quality of the pugs is.
As for aoe, many classes still have very effective aoe: demonology warlocks, fire mages, death knights etc. for example.