Steps to reproduce:

1. Open project from link below
2. Build to iOS
3. Launch on low end device like iPhone 4 or iPad Mini 1
4. App will shutdown after some time while loading

or

1. Create new project
2. Add new script with AudioClip list
3. Add 5 or more soundtracks to list
4. Build to iOS
5. Launch on low end device and it will fail loading

Closed as "By Design":
Depending on settings used on all 6 audio clips, memory usage is:
Decompress on load + preload (what's used in repro project): 600 MB
Compressed in memory + preload: 116 MB
Unchecking "Preload Audio Data" for either of two or selecting "Stream" gives a bit over 18 MB memory usage.

So it looks like the answer is to use the proper settings for audio clips for such use cases. If you ask to preload and decompress them, you can get a very high memory usage, which is never good on mobiles.