Curious what other 1520 users have for system storage. I'm up over 10 GB. I'm at capacity on the phone and whatever I delete or move from the app storage on phone gets filled up by system storage eventually.
Microsoft got back to me. The solution is to do a system restore.
That's not really a solution, just poor customer service on the part of Microsoft who should be looking into a real fix for this. I have a 1520.3 and am now at 6.79GB and still growing, clear internet cache and temp files regularly, don't take a lot of pictures or videos or save email attachments but it still keeps growing. Yet another thing Windows 10 will save us from, I'm sure.....