Have the foliages been placed through the foliage instanced tool, if not how much do they number in the scene (no of off foliages) , if placed through instanced foliage what are their resolution.
The process of figuring the pain point is to isolate which object is causing the issue and then solving it.you mention in your question that you feel it is foliages , did u try removing them and baking ?
Scene still gets stuck.
I would advise you to remove and try to pinpoint the pain point.