I rarely post but I will give it a go
I tried this method with 3 characters a monk, a wizard and a demon hunter and my experience is as follows:
Monk - Wizard: low level with a small array of possible builds proved nigh impossible for me (should be possible in a couple of levels)
Demon Hunter: at level 13 with decent gear and after a few failed attempts with whimsy builds I managed to start killing things in a respectable speed to make i viable. By level 15 (when I upgraded my gear in favour of speed) everything including rare spawns where a breeze. Come level 25 I went straight to NM (soloed diablo easily but cheesed my way directly to him after Act1) with another gear upgrade and about 1,700 dps the mobs melted and the speed is awesome. But I am having some problems with some elite pack combos (mortar/teleport), I believe that is every glass cannon's problem
So anyway thanks for pointing out this awesome way of leveling and to the nonbelievers... try harder!!!
Btw could you post the starting point of the build you used with your monk at level 15 (with or without gear stat choises)