Ok, some things first:
1. If you're expecting the best from lightworks by setting everything "ON" and at "100%" than you might get dissapointed. If this would be so obvious than Dwight wouldn't have to write the book about it. In the mean time try this:
- turn off sun
- set ambience at 50%
- turn off camera light
- try to use combination of 2 skyobject + sunobject
2. If the model is huge and shadow's quality is not your priority (but time is
) than - no lamps, no camera light just internal sun.
3. Settings help you get the reasonable result in a reasonable amount of time, but you need to make choise what is more and what is less important in your presentation.
Hope this helps a little.
Cheers