What are the best solutions for simplifying an assembly in SolidWorks?
Check the parts Feature Statistics and look at the time(s) listed.
Make a de-featured configuration of the parts with the longest rebuild times. To de-feature suppress what you dont need in the assembly (eg. fillets chamfers...etc). Update the assembly to use those new de-featured configurations.
You can do all the lightweight parts (icon is presented with a pen next to the name part), or use speedpack (a useful feature in low and when the computer does not need internal parts), and of course a very truncated configuration details (repayment of facets, some fillets, holes, etc. etc.) - is useful in calculations and simulations
You're going to lose any functionality, but solve as rigid for assemblies with multiple subassemblies works pretty well. This is a way "in SolidWorks" to simplify an assembly.
To answer the asked question, THEE best way to simplify an "assembly in SolidWorks" would be:
A) Buy a better computer