Watch SE, iPhone 7, iOS 15

1-Man wrote:

Does Apple in this case allow the watch to NOT update its OS?  

You don't have to update the watch if you don't want to.

Once the watch updates its OS, there is no turning back? 

That is correct.

 And for that matter, with the defects and stories about iOS 15 update on older iPhones, it may not be worth updating to iOS 15 in order to activate the watch.  Are there known issues still, with 15.8 now?  

You will always see more complaints about particular versions of iOS in these forums that you will see people saying they have no problems because this is where people come when they have a problem. People who are having no trouble don't generally stop by to post "Everything's peachy! Bye!".

1-Man wrote:

Ok thanks. if pairing with iOS 16 it does require the update to OS9 or will not proceed, so take it that is not the case for iOS 15 from your response.

All I said was that you do not have to update your watch unless you have a reason to do so. It's up to you to figure out which system software versions will work for your devices and if they are compatible.

If the 15 update on that older phone model drains its battery more or slows it way down and this is a known issue,

But it's not a known issue.

Restoring the phone is out of the question.

I'm not sure how restoring the phone is related to your issue but I also don't understand why a basic troubleshooting step should be out of the question if required. As long as you regularly back up your phone, it's not a big deal.

Well, I wish you the best of luck.