I sure hope it's better in 15. In my current iPhone it is just plain "eh". To be honest, it just isn't worth the price.
The problem isn't the head tracking. That works fine. The problem is that there is absolutely no surround to the sound. Nothing behind me, nothing in front of me. Just regular headphone sound going in a straight line from ear to ear through the middle of my head left to right. I'm comparing headphone Atmos to my 5.1 speaker system. They aren't even in the same universe. Not remotely close. Yes it sounds more bloomed out than standard stereo, but it isn't spatial by any stretch of the imagination. Space is three dimensional, not a one dimensional line.
I suspect a lot of people who are saying that Spatial Audio sounds fantastic don't have multichannel speaker setups in their home. They're comparing Spatial Audio to headphones, not a true multichannel rig. The whole point of Atmos is placing sound objects in three dimensional space- behind you, above you, in front of you... not just left and right. Dolby has played fast and loose with the definition of what Atmos is in the past. So much so in fact that some of the things they call Atmos (like sound bars) aren't at all the same as true Atmos. I suspect we're getting more of the same here.
I would love to be proved wrong in September. Then these $550 headphones and $1100 cell phone would be worth the price. Naturally, we get to wait until the return window is long passed before we find out one way or the other.