A path upgrade

[zabadabadoo]

FYI. Devs mentioned "direct upgrade patch" in second part of this post.

The Road to Zorin 16

It appears that you may have altered the base repositories or modified a system configuration file to unofficially enable release upgrades. We would strongly recommended against performing this upgrade as it's likely to break the system. We're planning to introduce an official direct upgrade patch from Zorin OS 15 to 16 a few months after the initial release of Zorin OS 16 this summer, after a thorough testing period has been completed.