@markalexa If I have it right the original Canonical Ubuntu Touch was based on 15.04. Which was the starting point for everything. As that came to an end and UBports came into existence it became apparent that 15.04 was to old, updates would end, security was becoming outdated.
Thats why the move to 16.04 was required. When that is completed UBports Ubuntu Touch will have a secure long term base to move forward on and regular OTA's, and other updates will follow.
16.04 is apparently a very different beast to 15.04 (I'm no developer so can't speak personally ) which is why things are taking time to make sure all is OK before release.