IOS 15 download on iPhone X

Download speeds are dependent on a number of factors such as your internet speed, current bandwidth usage, and server load. In my past experience with brand new iOS releases (iOS 13, iOS 14, etc), the download speeds for iOS updates are quite slow on the first day they are released. This is likely because a large number of users are trying to update simultaneously. If your download speeds are currently slow, you may want to try updating later or tomorrow.

It took about 30 minutes to download and fully update my iPhone 12 Pro Max. Your speed may vary depending on many of the conditions posted above.