yes i'm looking into it.
afaik there's 3 light types in unreal, moveable stationary and static.
static lights are the absolute cheapest, and cast no dynamic shadows. i switched the moonlight from stationary to static, since it didn't cast dynamic shadows really well through the windows. instead i've switched a fill light i have behind the windows to stationary instead, so objects moving in front of the windows actually cast a shadow now,
although the shadow doesn't connect with the legs so it looks like the character is floating.
not happy with the garish specularity on the walls. i tuned up some of the foreground lights, but it caused the walls to appear like water, so i'll have to do some material tweaking
here's a picture showing off the light complexity.
it is clearly higher in the entrance than the starting area, so i think this is part of the reason why there's a slowdown there.
i also had a dust foreground shader in the entrance area, which i believe was causing sever slowdowns, so i removed that.