I have a LG G2 Mini and a few weeks ago, I got a notification asking me if I want to update to Lollipop - I did it and, to my surprise, a few days later all the apps stopped updating screaming that there was not enough disk space - being confident that there is at least 3GB free, I went to the settings to check and... there was only 400MB free, with "System Data" folder under "Other" occupying 5.2GB (out of 8GB my device comes with).
This state of things has persisted ever since and, as a consequence, my phone is really laggy, apps crashes often and I can't even update anything. From what I googled, some people had this problem as well on various devices but no one came up with a definitive solution. I've tried zeroing the apps cache but to no avail, it only freed 30MB or so.
What can I do with it, apart from the ever-present golden advice of a factory reset? I would prefer not to root either. Is there anything I can do, then?