Working in chunks is your best approach to try an isolate what objects introduce the performance hit.
Your model is large in terms of scale with lots of reflective surfaces and internal voids to calculate light. It's probably a perfect storm where a realtime render engine like Lumion shows its weakness.
If it was me I'd be hitting up their support. A file like that should not bring it to its knees.
I'd give it a spin in Twinmotion to see what that does. Its 1/3 of the price and now that Epic owns it you get access to Megascans and other goodies too. Plus the Datasmith plugin for SketchUp is solid.