The lightmap density seems at least comparable to other Epic samples, like this level from Unreal Tournament. My expectation with a lower resolution lightmap density would be blurrier, less accurate baked shadows, but you can see in my example that there is a lot of noise coming through in the the bake.
This scene does make use of light portals to allow extra directional light and sky light bounce, but most of the interior light is coming from a lone spotlight on the ceiling. I am including a shot of the light settings as well