iPhone 15 how to return iOS 17 instead of iOS 18.3?

Try a Forced Restart and see if that helps, because you CANNOT go backwards in iOS. Downgrading has never been supported. I can tell you iOS 18.3 made absolutely no changes to my iPhone whatsoever in any of the areas you say it did for your phone.

Here is how to Force Restart (something I do after EVERY iOS update anyway) --> Force restart iPhone - Apple Support (CA)

Go to Settings > Accessibility > Face & Attention > Do you have Attention Aware Features turned on?

You have a one year manufacturer warranty on your iPhone. I'd suggest you schedule an appointment at your Apple Store Genius Bar for evaluation and let Apple help you in person.

Hi, can you help me out in one thing?

I own an iPhone 15, I guess after updating to iOS 18.3 I have encountered yet another bug or glitch. My iPhone ringer volume is not lowering automatically when a call is coming and I am lifting my iPhone 15, which worked fine until a few days ago, anyone else facing this?

Yeah, my screen on time has also decreased a lot. I have just recently switched to an iphone from android. And to be honest, the hype is not worth it. I have recorded videos as proof of glitches, bugs, and crashes on facebook, instagram, whatsapp, and twitter. And now this ringer volume glitch. Oh god, wasn't expecting this ****** user experience after switching, and that too all within 4 months.

Yes everything is turned on, its as same as before. I have already tried restarting my phone as well.