In theory that is correct, but there must be some other factor at play here, because the reports of "the exact some operation, at the exact same config, side by side, in the same room, with the same power dynamics, etc" of 15PM vs 14PM shows the 15PM very regularly thermally throttling (a test I did with a near brand new 14PM b/c I had an AppleCare+ replacement a mere week before my 15PM delivered, so it was not a worn battery that was somehow performing poorly impacting thermals because it had degraded or whatever).
The teardowns are leading people to guess (in an actually somewhat informed way) that the practical reason is that the surface area for both heat absorption and heat dissipation has been reduced in an attempt to further reduce weight (e.g. not just rely on Ti being lighter, but putting less of it in the device period, meaning the rudimentary passive heat pipe design has less of an effect).
What is maddening to me is that there is no way this wasn't caught in testing or even design. The world's most talented and well-resourced teams are working on this product with decades+ of product and market knowledge of this very specific product.
Adding insult to injury is that the move from Al to Ti was *completely* unnecessary. It has zero practical impact (no one, with a straight face, can say "oh yeah, my 14PM was WAAAAY too heavy, those few grams they shaved off are life changing"). On the other hand, throttling and absurd thermal issues are completely impactful to the core, singular purpose of the iPhone.
Here is a picture of my brand new, amazing Titanium iPhone 15 Pro Max in its preferred habitat simply trying to sync the days iCloud Photos (seriously, wasn't even using wireless charging and Photos paused sync because 'iPhone needs to cool down', and I live high in the mountains, where it's already getting down into the 40s and 50s....yet, this is the only way I could get it to actually perform something as basic as an iCloud Photos sync of the day's photos).
"Only on iPhone". hahahaha.
Stainless Steel has a thermal conductivity of around 14.3 ± 0.2 W/m K. Depending on which alloy.
Titanium has a thermal conductivity of around 22 ± 2.0 W/m K. Depending on which alloy.
Aluminum has a thermal conductivity of around 230 ± 10.0 W/m K, again depending on the alloy. This is why it is used internally.
So what does this mean? It means that Titanium is marginally a better conductor of heat away from the internals when compared to Stainless Steel. It means that the case will potentially be hotter at the same processing speeds, but the CPUs will likely be cooler.
So the titanium is marginally helping the functionality of the phone and will allow the phone to run at higher speeds than a Stainless Steel case.
