It’s not so bad. I actually had the opportunity to fly passenger in a real life Vision Jet a few months ago. Admittedly I was wearing headphones (certainly not those fancy Bose A20’s) but as I recall even when I took them off to speak to the other passengers the engine noise wasn’t overwhelming.
I do like the way FFX have implemented some little features for added realism but if there’s just one I’d really like them to remove it’s the aircraft cover. I have it on good authority that it is rather difficult to get into the jet with the cover still on, and even more difficult to remove it yourself from the left hand seat.