Issues Processing NC programs

I am experiencing issues while processing NC programs using the Production machining extension. Small parts work fine, but large parts with complex surfaces, such as molds and platens for seats (~6" x 26" x 26"), cause the system to slow down incredibly. There are occasions where it takes hours to run a material removal simulation. 

Is anyone else doing this type of work using the production machining extension? If so, what are you folks running for PC specs and do you have any other tips? 

Thanks,

Philip