monterey 12.6.3

you're right, it shouldn't take that long. but you may have caused an issue when you interrupted it during your first attempt. here's what I would try:

1. open your applications folder and move "install Monterey app" to the trash.
2. empty your trash.
3. restart your Mac.
4. start the upgrade process again, but don't interrupt it this time. let it run it's course.

As @jefferythefrog mentioned.

The are several Pauses and the clock seems to freeze.

15 Minutes is 40 minutes ( maybe ) 10 minutes maybe 30 minutes and 5 Minutes ( drum roll lol ) seems for ever and can have a coffee and come back and almost, Yes done.

Very much agree with @jefferythefrog.

Have upgraded and update 3 machines from Big Sur macOS 11 to Monterey macOS 12 and the longest amount of time it took was maybe an hour.

When I say 1 hour, I count from the moment I started to download to the Final Reboot with the successful installation.

Common issue is often some Third Party Security Software installed and messing up the whole system.

when you see "15 minutes to go", how long are you waiting before trying to intervene? that 15 minutes can in actuality be quite a bit longer than 15 minutes. sometimes it can be 40 minutes or more.