Apk size

Hi, I'm having issues with my games, some of them are very simple and still are over 6 mb, I don´t use a lot of images. I see other's people games and have more content by less megabytes.
And also sometimes my games crashes when starting.
My two games are on the play store, one is called Flappy Boo and the other is called Roll it. (By Youngle)