Clockwork (at least in my experience) is absolutely correct. Most of the environments I’ve used are made to look as pretty as possible without the thought or care of how they could be interacted with or explored in a gameplay scenario.
An example is one pack where there are HUNDREDS of lights, many of which do virtually nothing, that have HUGE attenuation distances. The optimization view of the lighting shows the entire scene to be bright-purple/white. It would run at around 50FPS, but when I delete and optimize the lighting, the FPS jumps up to around 120.
So, you’ll need to do a LOT of work with most of the assets.
So far, the most optimized assets I’ve come by are from FRESHCAN. They’re expensive, performance-wise, but VERY well optimized. I found that I could do very little to gather extra FPS/MS.
If you want tips on optimization, you can check out my list, here:
I’ve gotten very good at it.
Good luck.