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).
This echoes my own experience, too. It seems that people do seem to have vastly differing experiences of this part of the game, so either it's rather random or its difficulty is heavily skewed towards one's level.
But in short, my first experience, probably late 20s, was absolutely impossible and I had to give up and sulk for six months. The second time I was just a few levels higher but before I knew it, it was over and I found myself thinking "is that it?"
