Apple has released iOS 15.8.1 and iPadOS 15.8.1 updates for iPhone and iPad models that are not compatible with iOS 16 and iOS 17. If you have one of these models, then you can now download iOS 15.8.1 on your devices.
Along with iOS 15.8.1, Apple has also released iOS 17.3 and iOS 16.7.5 for compatible models.
iOS 15.8.1 is a minor update that brings security fixes for iOS 15 devices. No new features or noticeable changes have been introduced in this release.
You can download this update over the air by going to Settings -> General -> Software Update. If you want to install the update manually, then you can download iOS 15.8.1 IPSW and iPadOS 15.8.1 IPSW using the links below.