I don’t think it has anything to do with the version, since I am on 14.1.x and I don’t have this problem. The easiest way is this:
du -sh * | grep G
will at least enable you to filter by gigabytes to concentrate on what directories have the largest amount of data. If it is not the backups directory consuming space, then it will most likely be your repository data. In which case you will probably need to allocate a lot more disk space to your server, if there are a lot of commits being made each day with large amounts of data.
But only you will be able to tell what activity is happening on your server, whether it is because of commits and large repo data or not.
That should at least help you get started to filter down each directory and go from there.