If you've got your private keys or can find a way to export them in core (try and search for the fastest way).

You can import them into electrum or other wallet software that won't require full node sync (it syncs but it takes about 5 minutes on a very slow machine).

To activate pruning mode itself uou need to ender a number larger than 4000, so you can set it to 4000 and it should activate. If you go down the pruning route, to check it works start core and leave it running for a bit (until the loader screen goes) then close it and check the debug.log file in your data directory (where the config file is) and see if pruning mode has been enabled.