If you program using the built in api only (this means the functions available to the target sdk, nothing newer) then your app size will be basically all assets, as code is very compact by itself.

But of course, coding is by far more complex, you are like doing native programming (although easier than c). My apps are small tools, so I can.

Oh, and don't use Kotlin. It's a wonderful language and far better than java, but horribly optimized.