Following the release of iOS 15.0.1, Apple has stopped signing iOS 14.8. This means it is no longer possible to downgrade your iPhone from iOS 15 to iOS 14.8.
Apple usually keeps the signing window for an older version of iOS open for about a week. This time around, the company has closed the signing window a bit earlier than usual — iOS 15.0.1 was released last Friday for all compatible iPhones. Nonetheless, if you are on iOS 15 and were looking to downgrade your iPhone to iOS 14.8 for some reason, you are out of luck now. The only way to downgrade to iOS 14.8 is if you have saved the necessary SHSH blobs.
Apple is currently also signing iOS 15, but that contains more bugs and issues than iOS 15.0.1, so there’s no point in downgrading your iPhone to it.
If you have not yet upgraded your iPhone to iOS 15 due to bugs and stability concerns, you should wait it out. While iOS 15.0.1 does fix a few major bugs with the OS, there are still a lot of other issues that Apple needs to address. Until that happens, you should stick to iOS 14.8 on your iPhone, especially since there’s no way to downgrade to it.
There’s no jailbreak tool available for iOS 14.8 or iOS 15, so you don’t really stand to gain anything by downgrading your iPhone to iOS 14 or by not upgrading to iOS 15.
Did you downgrade your iPhone from iOS 15 to iOS 14.8 due to bugs and issues? Or were you planning to do so?