I know. The next update will cut this in half. Google is phasing out the use of its copy protection feature (which doubled the size of the application). I have switched to using their new licensing feature instead.
Roughly 90% of the game's size is due to the music files and sound assets (and they were reduced in quality even).
Additionally, for Android 2.2 (Froyo) users, you will have the option to install the application to the SD card.
So you can expect the game's size to be reduced to around 7MB. Which I still think is slightly high. I am considering removing a song. I just have to decide which one I like the least...