I managed to separate each level into a scene. That makes it possible to bake light and occlusion into the scene.
I had some problems learning which parameters work best.
The baking time was a marginal issue because my own computer only has a GTX1080 installed.
The next problem to solve was the sheer size of the level. The initial lightmap for FireboundForge had a size of 5GB. But overall, I’m satisfied with the results.
In this video, you can see the comparison between old and new.
The BloodshedArena has directional light from the sun. 
SludgeMadness now has a dusky atmosphere. 
Additionally, I added the Training Ground where, you can experiment with builds and spells. 
There is also a complete overhaul of my blog/product page of Raiding-Zone. The web version of the game is now available at Play.raiding.zone.
