Hi TiAm and volkiller730, and thanks for the answers.
Yes, I sure updated to the new beta, but it doesn't change much, as the former "Android" export already exported only .ogg files.
I didn't minify the script because I'm using cranberrygames 's Phonegap IAP plugin, for IAP in the game, and (unless there is something new) it requires not to minify the script.
I also already optimised all images' size in order to reduce the image number as much as possible (back when there was the number of image bug in XDK), I used ImageOptim to reduce the file of all exports, and I sure put into the .jpg format all the images in which I don't need alpha channel.
The current size of the image folder is 38 Mb. The media folder is 8,35 Mb but it features 128 Kb/s audio for music. The reason is that as I have orchestral music I'd like them to sound good. But if I really can't use the APK extension package, I'll sure reimport the whole thing 96 Kb/s which should make me gain about... 1,5 Mb... Still 18,5 Mb to grind !
Do someone knows if App expansion files are usable with any of C2's exporters (preferably XDK)? Maybe IntelRobert has a clue ?
If it isn't the case, I'll be down with TiAm's solution of schrinking graphics... :-/