Manual You Can Update your IOS15 Without PC.
1,Turn on the Device
2, Start at your Home screen
3,Tap Settings connect your iPhone with Wi-Fi
4,Your Battery will be more then 50%
5, Tap Settings >General > Software Update.
6, and then you find "download and install"(395.2MB)
7,click on "download and install"
8, you find "Terms and Conditions" click on Agree > Downloading will be start
9,downloading will be complete in few minutes
10,your device will restart
11,software will install wait few minutes and you get your device ready