I first tried deleting old apps and app data. This helped a little. I then deleted all of the music off my device which freed up some space but not a great deal. Next I opened the Battery Doctor app and ran the clean up scripts included, which clean out old cache and orphaned files. Again, this gave me a few extra MB but nothing noticeable.

The final thing I tried was to disable iCloud music under settings > music. As soon as I returned to check the storage space available I could see I had quite a bit more free. I checked back 5 minutes later and I had gone from almost full to 2GB free. It would seem that the caching of music on the iPhone with iTunes match is very inefficient on smaller devices. I see the benefit of caching music files for quicker retrieval & a reduction in cellular usage, but on smaller devices this really doesn’t help and I do wish they would include a way to disable caching, or a cache time-out.

If you use an Apple iPhone or iPad along with iTunes match/iCloud music I would advise giving this trick a go. Turn off iCloud music and watch your free space return. I now do this on a regular basis to free up space & delete the cache. It has really helped me free up space & made my 16GB iPhone much more useable.

If you are having the same issue please do let me know. I would love to hear your own fixes for storage issues on smaller iOS devices. iTunes match & iCloud music library seem very under-optimised in iOS 9 & I do hope they invest some more time & effort into improving this, especially on 16GB devices which I assume they will phase out in future iPhone & iPad models.