Ok so I got the Sunken City quest when I was level 11, now I'm level 44 and I still haven't beat it! I don't know why, but I think it's because I never made time for it.
You should be able to solo Sunken City now that there aren't any automatic street battles. If not, you can usually find others if you cruise the Crowded realms. Your Ice Minion will be helpful.
On my first Ice wiz I did Sunken City at around level 15 because it seemed like I was supposed to do it before going to Krokotopia - and it was tough. With all my other wizards I have skipped it and Tomb of the Beguiler and then came back after I was a Grandmaster to complete it. I usually join a group of players that are under level 20 and help them cruise through it. A lot of new players think it has to be done and don't realize it is just a side quest; or even know how much harder it is than the rest of wizard city. There really isn't any compelling reason to complete it when you receive the quest so I advise people to wait until they are a higher level when they ask me.
Anymore i just let it sit in my quest log until someone else asks me to help them with it. Otherwise, the only reasons i see to do it are for the level 38 life spell quest (dryad) or if i need red mandrake for crafting. -eli and crew
Its kinda long, but easy. I was lvl 17-18. I had someone help me and now I can solo or help :D. And Ice has tower shield. You can use your tower shield =) Sry if i was a little harsh xD