yes. ancients will take you to lvl 21. so from 21-25, you should do cows. a few games is all it takes.
also, the fastest way i've found to lvl from 10-20 is to kill all the scarebs (lightning bugs) in the area before tal rasha's tomb - canyon of the magi if i remember right. they die with one hit and give good experience. but you'll probably want to be wearing full sigs with a couple cheap lightning resist rings or else you'll get zapped.