I'm not really that up on MR, im still learning, but i dont think that your scene is that poly heavy at all. what's your poly count at the moment?
Try setting it to preview final gather or something like that and look in the output window and see whta it's telling you. It may have some information that will tell you why it's running so slow.
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB