The very first room of Arx Corinium is a gauntlet. Can you post what the group composition was, and any other relevant details?

You could try sneaking through, but that would only bandaid the problems you had; there are harder fights in that dungeon. You need to make sure that everyone is using an AoE bar for that fight, and you need to make sure that they're overlapping to knock down enemies really quickly. The tank should be using Cleave or one of its morphs, the DK should have a Standard ready for emergencies, etc. As a fellow sorc, I would make liberal use of Lightning Slash and its morphs (I use Flood), Critical Surge if you have it, and your favorite weapon AoE. Charged Atronach or Negate Magic are your best choices for ultimates.

The fight is hairy, but with a little focus fire its more than managable. If each member has a way to heal themselves and take some pressure off the healer, all the better, and make sure to interrupt those Lamias whenever you can.