Yes, you can upgrade from Z 15.3 to 16 but not yet. It will be available soon.
About paying full price again, I fully agree with @337harvey .
At least, that is the minimum what you can done, if you want ofc.
This work for 2 people is really huge. Making new builds, maintaining servers, forum, apps, mirrors etc.
I know that all of us paying daily for unnecessary sh*ts (junk foods,drinks, etc)
Imagine if you spend months working hard on something, and nobody even thank you for that.
But yeah, everyone have different opinion.
Even mine was , hell why I need to pay something on Linux, it is free..