I wish Godot allowed for smaller file sizes. The very lowest I've seen someone get a project down to is 10 MB. It's a little disappointing when your files work out to barely a few megabytes.
You can disable dome features of Godot by using a custom build of the engine. I did that for my F-Droid builds, since a F-Droid build recipe builds all dependencies from source. But I don't know how many MB I saved.