My apk is too big

Hello,
I am trying to hone my skills in making a multi level stencyl game. My game has one "intro" or mainpage + 14 levels.  All of them are separate scenes.  My game's size is 800x480 px (same as my Android device).
As backgrounds, I have chosen 15 different pictures/images, each 800x480 px. in size roughly apox.   200-270kb each, one picture for each level.

When exporting my game as an apk i get a very large apk file,  142 Mb in size, obviously too big to be used on mobile devices.

Exporting my game as a flash/swf I get a much more decent size, 7.45 Mb.

Does anybody know why my apk is so large (clearly is way larger than the sum of the jpeg files combined) and how can I shrink it down to size without losing the backgrounds or any visible photo quality from them?

Thanks in advance.

do you have any music?

So far no. And after observing this problem (and before posting in this forum) i have eliminated all my actors and other elements in an effort to get to the root of the problem, and basically all i'm left now is a game with 15 empty scenes with backgrounds as described above resulting in an 142 Mb apk

Assuming you created your art at 1x, you should set your max scale for Android to 1x.  By default Stencyl creates 1.5x, 2x, and 4x art and uses them for mobile, but that isn't useful if you created your art at 1x anyway.

Thanks, that was the issue, problem solved now.