I just updated from v14 to v16 and to be honest, really smooth process, no notes.
I created a clone database as suggested (it took a few minutes to come active). I then checked things locally against the clone and when it all seemed good I pressed the upgrade button. The instructions embedded in the UI were good and the automations all worked. The only issue was that the documentation was slow to load after the initial page load.
I'm not sure if there's much of a performance change and I'm not taking advantage of any features from it currently.