Okay, the first time I ever ran a VM, it lagged horribly. Recently, I ran it for a 2nd time, this time putting all graphics on the lowest setting possible, and the improvement was very minor. Is there anything else I can do because normally the game runs fine on my computer.
Since Vile Maw is filled with water, make sure all post-processing effects are turned off.
Also, since a lot of movement is going on in the first couple phases of the fight, go into the Social options and ensure that "Show Only Dispellable Effects" is checked. (This should be a big improvement for you in all fellowship and raid situations.) Otherwise, every time any player moves even one meter, all the positional buffs and debuffs for every player have to be updated. You don't really need to know about all these buffs and debuffs.
Turning off all names and floating damage/heals can also sometimes improve responsiveness.