Zorin os 15.3 is based on Ubuntu 18.04. You would be down grading your server to a previous version of Ubuntu and previous version of the Linux kernel. I would suggest waiting to use Zorin OS 16 lite that is based on Ubuntu 20.04 when available. It would be best to do a fresh install of Zorin OS on your server and backup your data before starting the zorin os 16 lite install.