For the PNGs, try encoding them as 8-bit (paletted) rather than 32-bit; the quality will suffer a little but I’ve found it to be a very effective way of saving space, and in most cases I can’t see any difference. There’s an online tool to do that here.
For the WAVs I would convert them to MP3, which should be much smaller; you can choose the best compromise between size and quality. If you don’t already have an MP3 decoder in your app dr_mp3 is an easy-to-use header-only library.
That’ll help for now (I wonder if saving my WAVs as OGGs will save a bit of space - or do they get compressed in the .abb file anyway?), but I’m planning on adding another set of maps to my game so there’d be no way to keep it all below 150MB. I’ve managed to get it below the limit for now, but only by taking out all the British, Italian, French and Japanese voice acting I just paid to get done (only leaving American, German and Russian).
I think there’s a way to have the media files downloaded separately so would be great if anyone’s done that and could help!
Yeah, use ogg, it often gets smaller than mp3. If you have audacity you can easily see how compressed you can get, lowering sample rate and other stuff