I noticed that my game of 3 scenes: Start Menu, Game, Game Over+Score scenes with very few sprites caused the file size to be upwards of like 50 MB. I am led to believe that Unity includes extra files that are increasing the size or I need to really optimize.
Do multiple scenes play that bad of a role in file size? I never paid much attention about the size of the file until I tried making games for mobile devices.
No, additional scenes cause very little overhead. It’s your assets - textures, audio etc. that use up the majority of your build, + about 15Mb overhead for the runtime libraries. Immediately after creating a build, look at the editor log for a breakdown of filesize of all the components included in the build.
You might need to compress your textures to a much lower res, also any audio assets you include are going to increase file size dramatically unless you heavily compress them.
As far as I’m aware added scenes shouldn’t increase the file size too much however you could try and making it so all your scenes load in just one main scene. In my opinion it would be best to do this as when developing for mobile I find loading between scenes takes an age (this might just be my device though)
Hope you find this helpful.
@kuos
check this link Unity - Manual: Reducing the file size of your build
well you can check which is increasing the file size clicking
Console tab ->Open Editor Log-> and look for these
Player size statistics
Level 0 ‘Assets/Loader.unity’ uses 459.0 KB compressed / 1.6 MB uncompressed.
Level 1 ‘Assets/Game.unity’ uses 2.3 MB compressed / 7.8 MB uncompressed.
Total compressed size 2.8 MB. Total uncompressed size 9.4 MB.
Textures 3.9 mb 41.2%
Meshes 2.3 mb 23.9%
Animations 679.1 kb 7.0%
Sounds 0.0 kb 0.0%
Shaders 538.1 kb 5.6%
Other Assets 653.8 kb 6.8%
Levels 147.8 kb 1.5%
Scripts 453.3 kb 4.7%
Included DLLs 136.0 kb 1.4%
File headers 747.4 kb 7.8%
Complete size 9.4 mb 100.0%
Used Assets, sorted by uncompressed size:
277.1 kb 2.9% Assets/Player/Human.blend
264.1 kb 2.7% Assets/Player/Orc.blend
216.1 kb 2.2% Assets/Monsters/Foo.blend
213.0 kb 2.2% Assets/Dungeon/Dungeon.blend
170.8 kb 1.8% Assets/Monsters/FooSkin.png
Then you can accordingly decrease the size.
Hope this help 
@tanoshimi I was able to locate the editor log, but I am still unsure of which files/elements are responsible for most of the file size.
– kuos