I'm still stuck at Hordes of Underdark,I know I know....but why is it so damn difficult?! The Valsharess one on one fight,and the Maugrim + many others fight,the fourth Guardian of the Path fight.....I cheated through all of them,still I wish I wouldn't have to...I found this one just impossible,I've already set the difficulty to "easy". BTW I'm a Sorcerer(16) and Monk(11).
I remember most of HOTU being quite easy, in large part because of all the over-powered gear, but I can be a bit of a "powergamer." Certainly the fight against Grimgnaw & co. can be quite difficult if you go in unprepared for something that intense (and you probably would be unprepared, since it is not like much of anything else in that module is at all comparable in difficulty).
At any rate, your build certainly does seem to be less than ideal. Among other things, having only 16 Sorcerer levels means you cannot cast 9th level spells, and are thus missing out on over-powered stuff like Time Stop and Maximized Isaac's Greater Missile Storms.
Also pay attention to what gear you are equipping. It is generally a good idea to max out your Armor with an item boosting it in every slot that gives a bonus to a unique type of Armor (since aside from Dodge they do not stack): Amulet for Natural AC, Boots for Dodge AC, Armor itself or Bracers for standard Armor, Deflection on ring, cloak, or most anything else, Shield...well, irrelevant in the case of your classes. With monk, furthermore, boosting both Dexterity and Wisdom (with item, spell, potion, or combination thereof) also increases AC. Playing a caster, you will want to avoid going into battle without first casting whatever buffing spells you have (In particular, Displacement or Improved Invisibility for Concealment can enormously increase your survivability). Also, once past the beginning of most modules you should have enough gold to purchase dozens of Heal potions. Have you done so? Are you using them?