Disclaimer: I don't own a real bike and I haven't ridden a street bike at all, only dirt bikes growing up.
That being said, I don't know how accurate MotoGP 15 is or any of the previous games, however I did enjoy MotoGP 13 and RIDE, MotoGP 14 was not that good to me. I'm really liking MotoGP 15, feels like the successor to MotoGP 13 which 14 wasn't.
I've heard complaints that its too easy for some people. I'm no alien bike rider and its plenty difficult for me. I think there's 5 adjustable skill levels and I have my hands full at medium.