I have heard of these iPhone 15 issues and have a 15 Pro Max that doesn't heat up too much... got lucky.None of you all have the new iPhone 15 Pro models obviously..........they get HOT, my Mojo 2 doesn't get hot, warm but not hot whatsoever. If you are using it outside then use a lighter colored cover to reflect some of that heat instead of absorbing it like a black aluminum shell will do naked. I use the Green leather Miter case with my MJ2/Poly and it stays at a temperature I am comfortable with, again my iPhone 15 Pro Max on the other hand gets hot to the touch when charging and on calls .
More to the topic of heat and MOJO/Poly I simply put mine on its side, balls up, when it gets warm and that seems to keep temperatures in check especially when charging while in use. Exposes more surface area for cooling. Desktop mode on the MOJO 2 is brilliant. MOJO original comes up short in that regard but I found the battery easy to change out thanks to posters here. Sourcing an OEM battery was another matter.
Using an original Van Nuys MOJO/Poly case modified to work well with either MOJO/Poly combination.
When mobile and the temperatures out are really high I don't want to risk my earphones being damaged by perspiration so I switch to AirPods Pro2 with the iPhone. Sound quality not as good but less ambient noise in trade. I believe the MOJO/Poly temps would be OK but not ideal. These are tough units and overbuilt compared to many consumer items.