Decrease the pakage size of android game

On Your Article:
Developing for Android and iOS with Unity3D: Lessons Learned
@ Ralph Barbagallo - VR, AR, XR, Game Developer and Publisher
i found an amazing thing that your game : Brick Buddies
@ :
is size of just “9.2 MB” it just amazing because when i try to make a simple game in android it does’t matter what i do the minimmum file size is 17MB so how you do that means how you decrease the file size to 9.2 MB .

I have this problem too, I resolve with this: Reduce APK Size