Is it an iPhone 15 thing? I mean, since iOS 17 update, my iPhone XS Max has been running very hot, it doesn't cool down unless it's locked and nothing is happening on it. 10 mins of use (add a Calendar event or logging my mood on Health App, simple tasks) would kill about 15% of battery, battery health went down after a few weeks of usage from 82% to 79% .. I've never had this heat/battery drain problem before on the same device.
Also, iPad Pro M1, it's been always cold to touch (very cold), now it gets warm on simple tasks after iOS 17. Just warm though, can't say it heats up.
My watch (Series 5) also, after WatchOS 10 update, it became like a wrist furnace. It literally just fires up randomly on my wrist without anything I do, and not to mention, battery life just dropped under 80% after the update. First to 73% and now on 75%. And it's hot like half the time, never felt that heat on my wrist before WatchOS 10.
I have to charge my watch twice and my phone 2 or 3 times a day now after the update. And it's been like that since the Betas.. I've factory reset / restore the iPhone and the Watch once the official release was here thinking it might help out, but nothing. And I'm sure it's not indexing, I mean, it's been a month now or so, indexing for a month?
Also I've updated all of the Apps, and those who didn't get updated after iOS 17 release are currently offloaded. So it's not an app optimization thing either.
Reading a lot of the comments here makes me wonder if it's 15 thing, a lot of you are stating exactly the same symptoms I'm having with older devices. Also, I have to mention, software is running crazy stable on the devices I've mentioned, I mean, drastically more stable than iOS 16. Which makes it sound like the processors are pushed to their limits for performance which is affecting battery and causing heat? Just speculating.
And yeah, let's hope it's just software after all that would all be fixed with an update. I was planing to jump to 15 as soon as it's available in my country, so hopefully I wouldn't be purchasing a malfunctioning hardware after 5 years of wait.
Advice: For those who'll keep their devices and wait for an update that may or may not fix things. Try to do everything so as not to kill battery health too early. Charge with slow wired chargers like the old days, wireless and fast charging generates heat. Don't use your phones while charging like ever (for now), and keep it always in cool places at least while you're using it. Hopefully an update would fix things up and you'd be back to your normal usage behavior.