If you want a small game, write your own code, or use a small engine like Gameplay or whatever.
Unreal Engine, the engine itself, has significant size, because it includes code and resources for a bunch of features, that you may or may not currently be using.
Unreal build generally like a large monolith, and cutting out the bits that YOU don’t use, is often somewhat hard.
The good news is that, as your game grows, and uses more features, you won’t have to pay extra for those features, because they’re already part of the engine.
Finally, as Chris said, UE now supports OBB files, and the default Android build does generate an OBB for any bigger resources you use.
And, in current version, it even downloads the OBB for you 
Another way to look at this: If you’re not planning on making at least a 200 MB game, targeting high-end devices, then why are you using Unreal Engine?