Today Apple released a minor update to iOS and iPadOS 15, bringing the version numbers to 15.2.1. In addition to some security fixes, this update addresses some bugs related to photos shared in iMessage and some problems with third-party apps in CarPlay. Even if you aren’t experiencing these specific bugs, I recommend installing it right away because of the unlisted security updates.
To update each of your devices, go to the Settings app > General > Software Update.