What does the 'Levels' data include in the editor build log?

I have the following editor build size report in my editor log:

Textures      40.0 mb    33.9% 
Meshes        17.6 mb    15.0% 
Animations    0.2 kb     0.0% 
Sounds        9.4 mb     7.9% 
Shaders       68.9 kb    0.1% 
Other Assets  64.6 kb    0.1% 
Levels        46.2 mb    39.2% 
Scripts       124.0 kb   0.1% 
Included DLLs 4.1 mb     3.4% 
File headers  406.9 kb   0.3% 
Complete size 117.9 mb   100.0% 

What does the Levels include? I guess it's saving positions of the level assets. But why is it so big here? This is an iOS build. I assume it's either occlusion data (but this is only an uncompressed 1mb for each of my 3 levels).

It might be the 'Static batching' option? However, disabling this option does not reduce my build size (cache?).