imac 27” late 2015 Wi-Fi 6 or 7 upgrading

There are two questions:

1. Why do you believe that macOS Monterey would provide support for any Wi-Fi 6 or 7 radio when the Late 2015 iMac never shipped with that class of Wi-Fi radio? Even a 2020 iMac shipped with an 802.11ac (Wi-Fi 5) radio.
2. Adding a third-party USB Wi-Fi 6 or 7-capable radio still does not address the operating system lacking that radio support for your model year iMac, or even that third-party USB radio. It would require that USB radio to install software supporting its Wi-Fi 6/7 radio. You had better check which macOS operating system version that third-party radio supports before purchase.

The Wi-Fi card on a 2015 model is removable and replaceable. The real question is whether you are prepared to disassemble the Mac entirely to access the card and whether you can find a replacement that supports Wi-Fi 6 or 7 out there.

Apple won't replace it for you if that is what you are asking, and they won't help you if you mess something up.

May be simpler, to just get an external USB Wi-Fi card instead of messing with the internal one.