Perhaps a member of the Zorin Team can clarify things.
Are you able to post a link to the Twitter account that stated that Zorin OS 12 can be direct upgraded to OS 15?
The Ubuntu Universe repository is huge. And I do mean HUGE. While Recent releases of Zorin OS contain the sources for the Zorin OS stable repo ( and I link to the Zorin Repo on occassion), I wonder if ‘how something is worded and how it is interpreted’ may be a factor in this topic.
The Zorin repository contains everything you will find on Zorin that comes with Zorin. But a complete replacement of the Ubuntu Universe Repo?
I am fine with being corrected.