Size of backup dropped after upgrade from Ubuntu 14.04 to 16.04

After an upgrade from Ubuntu 14.04 to 16.04 the backup size of a server dropped massivly, from 17GB in daily incremental to 1.7GB (size of tar.gz) The main chunk of the backup is a mysql database, which was 18GB when using tar -xvzf to unpack the tar.gz file of a backup from before the upgrade, while now it is around 1.5 GB

Is the following entry in https://www.virtualmin.com/documentation/system/backup-and-restore#toc-i... still valid for Ubuntu 16.04:

Enabling incremental mode for a scheduled backup is as simple as changing the Backup level option to Incremental. This will only apply to home directory contents - Virtualmin does not support detection of incremental changes to databases, so if your virtual servers have a large amount of data in MySQL, the saving will probably be minimal.

I'm still checking if data is missing, but due to the size of the files it takes some time …