I have an iPad 6 that I've held back to iOS 12 since it can sync with my iTunes on 10.10 Yosemite. I have a substantial and carefully curated music library.
I'm now upgrading to a newer computer running 10.14 Mojave (where I am stuck because I need 32-bit support for costly software and drivers for costly equipment I can't replace.) The computer can run 13.5 Ventura, but 10.14 is fine for my needs, and I don't want to break my workflow to reboot everytime I need to do a legacy thing.
10.14's iTunes unfortunately will only talk to iOS 15, not iOS 16 (or about-to-arrive iOS 17).
So here's my question. How do I get iOS 15 onto this iPad?
I have already downloaded the iOS 15.7 IPSW file from Apple, and placed it in my (Yosemite) iTunes' ~/Library/iTunes/Device Support/iPad Software Updates folder, and iTunes completely ignores it. Would it help to migrate my iTunes library to the computer running Mojave?