I did have motion sickness at first but got used to it quite quickly. It actually disappeared on the 2nd/3rd day of use I think. I have absolutely no problem driving race sims all day long if needed, I’ve been using my VR gear for 3 years now.
The trick is not forcing it -- the instant someone feels even remotely nauseous they should stop. If you the user starts actually feeling sick they're liable to sensitize themselves to motion sickness.