If I were lucky enough to get a flight in an F-15, I'd be disappointed if I didn't get the full 9g experience, sickness or no sickness. You're only here once, so enjoy it. If you're not happy with those conditions, don't get in the f***er, pretty simple really.
It's a once in a lifetime experience, to not take advantage would be like diving a Ferrari F1 car around a car park i.e. pointless