This is so cool! I'm thinking that your problem might be the volumetric spotlight which is flooding the entire scene with light. Try completely enclosing this scene within a cube, where the spotlight is within it, but light from it can only enter the scene through the window. Delete the sun and replace it with a point light or two, and that might help your shadow problem. You also might up the shadow intensity for certain point lights. I won't ever use a Sun or a Directional Light for an interior scene and I always isolate the scene from the rest of the "World".