the problem is that low res lightmaps doesnt look good. there are too many artifacts and noise. and baking on high res consumes absurd amount of memory.
is it possible to bake scene part by part? for example bake the floor lightmap first and then bake the walls separately etc? my computers doesnt support more than 16GB of memory so im really restricted.
In order to bake floor you need bounce light from rest of environment so you cant exclude it from calculations. It was possible to bake separate objects back in ue3 but lighting was much simpler back then