What level are you now? I tried this quest once in the late twenties, or so, and had trouble killing creatures fast enough, but didn't have any problem in the mid thirties (left this until one of the last things before heading to the Hall of Echoes).
There is no way to leave to get better equipment, etc, to do damage faster (other than reloading a save before starting to do the bottom section, and loosing those 5 levels).
What type of character are you playing? Any free stat or skill points you could use to tweak your build?
In D2:ED I stood a bit in front of Zandalor, with my creature summoned, and used a bow on opponents from the front two rifts (more to draw them towards me than to do damage, since I was playing a warrior with no archery skills), and occasionally had to Rush Attack a memory eater from the back rift.
