The way I think of it relates to people. V15 was like having a friend that will tell you everything you want to hear. The relationship is low maintenance and it was easy to get along with. V16 is like having a real friend. One that will tell you everything you need to hear, even if you don't want to hear it. The relationship is higher maintenance, but you can trust it because it isn't BSing you. Even though it is not as easy to get along with, if you stick with it, it can only grow into something better.
I feel that with V16, there is a real relationship between by guitar and the amp models. The amps react to my playing and in turn, I react back, sometimes in unexpected ways. The amp models feel like they want something from you, they aren't just there to submit. For this alone, it is worth the update I feel.