Can't update to 5.3.2, not enough space. Nothing left to delete.

Is there any way to clear up cache or temporary files? My watch has the 5.3.2 update ready but it can't update because it needs at least 1.8GB available, it has around 860MB. I've removed all the apps other than the built-in ones from Apple that can't be removed, and I've unsynced all podcasts, all music (though there's still 136MB of music on there for some reason, none of my playlists are being synced), all photos, mail, etc.

Even if I could clear out that music, it would only be about 1GB free, still well short of the 1.8GB 5.3.2 says it needs to install. The 5.3.2 update itself is taking up 1.3GB, which I could delete, but when it goes to update it's going to end up re-downloading and it will be right back to not being able to install due to lack of space.

The watch says it has a 5.3GB capacity, and the usage screen shows 2.2GB being used (1.3GB of that is the update), which means 3.1GB is in use but not showing up on the usage screen. Is the OS really taking up over half the storage space? Or is there just a ton of cache/cruft built up that hopefully can be deleted somehow to free up a lot more space that isn't showing up in the usage screen? I know on my iPhone I frequently see it builds up an "other" storage that isn't categorized and usually clears out when I do an OS update, so I've always assumed it is cache/temp files that empties out during the upgrade. It really should empty out whenever space is needed, not just during upgrades, or there needs to be a way to manually flush it out periodically.