The attached patch corrects the joystick axis INT15 support. The position as stored is a float (-1.0,1.0) so simply casting it doesn't do much. Canonical values are 0-1A0 for a 250kOhm stick but it seems 100kOhm are more common so I chose 0-FF. Also handles case of having one joystick active but not the other; this adds another conditional but if you want speed you're not using the BIOS anyway...
(note that if a program is e.g. reprogramming timers out from under the BIOS and expects this to "break" the joystick support in some particular way this routine won't behave like a real PC...but that's a pathological case and not worth worrying about).