Hans, Zorin 15 is built off of Ubuntu 18.04.
Zorin 16 will be based off Ubuntu 20.04. A release date has not yet been set, though there are rumors that it may be by the end of the year.
That said… I would not call 2 1/2 years to be “real real outdated”. On one of my computers, I am running Zorin 12.4 Lite, based off Ubuntu 16.04 Xenial.
While some things get updates that improve performance - Many things reasonably stay pretty much the same even with new releases. Be mindful of the trap of thinking “newer must always be better” and “Older Must be real real outdated and bad (or inferior)”.
A great deal of the time, most software is the same package with a new version number stuck on it.