Agree on that I build a fairly big scene from my home town just to test the engine and light build takes less than 5 minutes i build bsp brushes in the editor and imported some self made fbx meshes from blender.
Looks like you might have BP_sky_sphere in your scene this renders nice clouds but takes for ever and your inside a building so you dont really need that try disable that!
Scale nearly 1.1 as close as possible ± 2 square KM.
Used google maps screenshot as reference my city live there all my life.
Photo taken from my bedroom window.
://s15.postimg.org/jynnkaydz/1888642_1429839043926573_21948699_n.jpg
In game screenshot (W.I.P)
://s21.postimg.org/tno5v88v7/Capture1.jpg
Take a look at the lightmass importance volume some area’s are excludes.
://s11.postimg.org/xhqzi3qlr/Capture.jpg
Greetings,