[O'Sancheski]

Make sure that you have an adequate processor. Large assemblies will run much smoother if you have a good processor and a decent amount of RAM.

Also, another thing that will help with the lag issue is to make a lot of sub-assemblies. Rather than having all the mates/constraints for the whole robot in one assembly, make an assembly for each mechanism that is on your robot and then insert those assemblies into your main assembly.