I am having trouble with the battle itself and i'm also experiencing alot of slow down due to the amount of spell effects and enemies present onscreen. My party consists of a level 15 barbarian, level 16 anomen, level 14 imoen, level 15 nalia, level 14 vagrant, level 13 auramaster.

Just need hints and tips in doing the battle and just any advice on dealing with the slowdown.

Your party is a bit low level for that stage of the game. You have either sailed for spellhold a bit too soon with a low level party or have skipped the City of Caverns, yes?

My suggestion is that you go to the other side of the map to Mind Flayers' lair, Beholders' cave and Deeperdark dungeons. Clearing those areas will give you some xp and probably a couple of experience levels.

Both drow ambushes (specially the first one) are toned down in IA v6.