Transferred today from my 12 mini to the new barely yellow 15 (the yellow Al frame looks like gold to me).
Migration went without a hitch.
What none of the 15 reviews prepared me for is the tremendously better speaker. The 15 is so much louder and clearer than the 12 mini. Even driving, with Maps turn by turn instructions, the difference is clearly audible. Not to mention the difference playing music.
And although the 15 to me is still a gigantic phone, I am pleasantly surprised that it doesn’t feel at all heavier than the 12 mini. And that’s in spite of 36 grams more (a 27% increase). 
The smoother edges are nice too — cuts less into your palm or fingers. Especially important now that I really can’t reach far enough and tighten the grip even more in a futile attempt to get my thumb all the way to that other screen edge. And while trying realize I’m at risk of dropping my brand new fancy phone. So second hand indeed required here.
Camera bump is even more ridiculous, the wobble is as bad as before. But at least it’s not worse. And no, I’m not going to put on an ugly bulky case after I just spent $$$ on a phone master designed to be svelte and nice to look at. If somebody ever manages to make a svelte neutral case that gets rid of the wobble and has no lip whatsoever, let me know. Previous attempts have been entirely futile.
I’m not sure I’m a fan of the ever so slightly curved glass at the edges. It seems to me that curvature now gives me a thin edge of glare around the display even when there’s no direct reflections on the display parts I’m looking at. Has something a bit cheap/Samsung-y to it IMHO.
Dynamic Island is a fun gimmick. 
The frosted mug type glass back is really pretty. And it isn’t just looks, it feels just slightly rough too. Much easier to hold and feels real nice. I love how Apple hid the earpiece speaker between the frame and the screen. Just beautiful. 
I ended up also getting new APP with USB-C to replace my 1st gen APP (die Lightning, die!). And holy cannoli, the noise cancellation and audio quality is a lot better on these 2.1-gen compared to the 1st gen. Very nice.