First of all:
If this is your first try of LW than I can only congratulate.
Now some tips:
- your scene is not only about the lights, it is about how your lights interact with your shaders
- for the walls try to use more "diffuse" in your shader (I usually have 0.8 - 1.0), reflectance - matt, and as Dwight pointed - it is good to use displacement map also for interaction with light - start with value of 0.05 or -0.05, if you don't have one you can use procedural - "rough", amplitude 0.05, scale 0.05, sharpness 3, detail 3
- try to inrease ambient light, which is not very good but maybe you won't need to use extra sunobject to light up your wall from inside, I usually keep it at 48%, but you can try even 80%-90%
- less lights you have - more control of a scene, I don't think that skyobject have much contribution in an interior scene if you they cast shadows, I would rather increase quality of a windowlights
- maybe some more "specular" on the floor would be nice - but it is up to you
Hope this helps, don't hesitate to send your progress.