Can't update to iOS 15

You have tried “Everything” however you did not tell us what exactly you have tried. I am going to list a few things for you to check to install an iOS update. Some of it you may have already tried however I have no way of knowing that.

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.

angelvenegaslol Said:

"ios15: why does it not let me update? i’ve tried everything"

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Determining if an Update will Install:

How to do so...

A. Verify Compatibility:

Confirm the model of your iPhone. If iPhone model is incompatible with iOS15, then it is because you iPhone does not meet the hardware requirements for this iOS version(s).

To Find the Model Number:

1. Go to: Settings
2. Select: General
3. Select: About
4. View: Second item-down

B. If Compatible...

1. Back Up First:

IMPORTANT: If you have an option to update, however, then be certain you backup your iPhone first. That way, you will have something to restore your iPhone from should anything go wrong with the update

then...

2. Proceed with the Update:

Go Here:  Update your iPhone Using a Computer - User Tip

Looks good to me, but sometimes it just doesn't seem to cooperate.

You might consider connecting to a computer and updating through Finder (on a Mac) or iTunes (on a PC). I prefer that method because it does a complete backup before attempting the update and it requires less free space on an iPhone. Those updates are always complete installations and not just incremental pieces that are stitched into the existing iOS installation.

What model iPhone?

How much free storage space do you have left on your iPhone 12?

Axel F.