The game is already compressed down by 90%, the best that can be done without notable image quality loss.
Fans sometimes do further compressions, usually to get it below 2gB so they can make it an .apk for easier installation on android. Of course, these aren't official due to the severe quality loss.
Last I know of was v0.14 though, hopefully someone else has a v0.15 version for you, and future versions when available.