mad girlfriend...help! Macintosh OS issue

I recently upgraded my Macintosh operating system from 9.1 to 9.2.2
and it seems to have had a detrimental effect on our MYST 3 Exile! It
plays not too bad but then starts to slow down and the frames drag and
cursor jumps. This is the MYST 3 edition by itself , not the one thats
included with other mysts.
I've looked into Uninstalling the OS back to 9.1 but that doesnt seem
possible and havent seen any help on the MYST site for this.
After checking the back of the CD jewel case, i see it does say
Macintosh 8.1 to 9.1 !
My girlfriend is peeved as she is just getting deep into it (somewhere
in dank tunnels in Voltaic) and is demanding i fix it or it may be the
couch for me!!
any suggestions is appreciated