I can’t install iOS 15 on my phone

Welcome to the Apple Support Communities.

If you have a supported device, iOS 15 - Apple, and you still cannot update, see: If your iPhone, iPad or iPod touch won’t update - Apple Support.

Jack

Ensure that you have iPhone 6s or a newer model to update your iPhone to iOS version 15. iPhone models that are older, iPhone 6 and below, will not update to iOS 15.

Make sure that your iPhone is setup to meet the following requirements before you attempt to update the iOS version over a Wi-Fi Network. Open Settings ➡️ General ➡️ Software Update: If there is an update available for your iPhone then it will be listed here. Follow the on-screen instructions to download and update your iPhone. 

• Your iPhone must have a fast Wi-Fi connection; you cannot update over cellular data or a cellular hotspot
• Ensure that you do not have a beta profile installed from a previous version
• The iPhone can not be in Low Power mode
• The battery state of charge must be above 50%
• Your iPhone must have at least 6GB or more free storage space
• Your iPhone cannot be connected through VPN
• You should leave the phone plugged in until it finishes updating, both to assure that it remains above 50% and to keep Wi-Fi enabled (Wi-Fi turns off when the phone sleeps if not connected to power).

Axel F.