Install update iOS 15.5
iPhone 6s Plus
iPhone 6s Plus
I would restart the device, leave it connected to the charge circuit, then attempt the update again. Also see the user tip below for other possible causes.
Updating iOS: common issues and solutions - Apple Community
I would restart the device, leave it connected to the charge circuit, then attempt the update again. Also see the user tip below for other possible causes.
Updating iOS: common issues and solutions - Apple Community
Please read the message at the bottom of your screenshot.
Preferably leave it connected to the charge circuit during the update process.
Unable to install update
Install update iOS 15.5