PePPo, since nobody has mentioned it yet, you can try changing all your C2 graphics to 8-bit PNGs rather than the default 32-bit. Hopefully, this will allow you to publish now and give you more time to figure out how to get the assets from a server, from within the app.
This seems like the best solution to me. We've PNG-8 encoded our assets and we're sitting at <5mb for Mortar Melon, spanning 3 worlds with assets designed at 1080p.