Dungeon Boss (DB) is a Unity iOS/Android title I helped Boss Fight Entertainment ship this year. I recently wrote a blog post basically containing a brain dump of all the low-level memory related things we learned in the trenches while trying to make the product stable.
Due to the sheer amount of content and code, DB couldn't have shipped at all on our target devices without aggressively utilizing every built-in Unity compression option we could get our hands on:
- Audio: We found and modified a custom editor script that allowed DB's sound designer to fine tune the music and FX audio bitrates to the absolutely minimum needed. We gave more bits to music vs. sound effects. (It also helped that DB's sound effects purposely have a classic 8-bit feel.)
- Meshes: We used Unity's built-in mesh compression feature as aggressively as we could. This caused a few issues on map meshes that we had to work around by hand.
- Animation: We tuned our FBX Importer compression settings several times to find the best balance between visible artifacts and memory/file savings.
- Texture compression: At the last minute, we had to switch the majority of our textures to PVRTC 2bpp to free up as much memory headroom as possible. Without doing this DB was too unstable on lower end iOS devices. Quality wise, 2bpp looked amazingly good (much better than I expected).
- Asset bundles: We disabled Unity 4.6's built-in LZMA asset bundle compression, grouped the assets by type, then we packed the raw type-grouped asset data using a better compressor (LZHAM). Thankfully, there were enough Unity modding tools available, and Unity was flexible enough, that we could do this without having access to the source code of Unity itself.
Also see this page in the Unity docs for more info on how to examine and reduce file sizes of Unity builds.