My 2007 G35S has 23k miles on it (I don't drive it often - the joy of working from home). This is the first time I changed it and the stock filter didn't look too bad. It still looks pretty clean except for some small black particles. I wouldn't have change it yet had I known it wasn't that dirty, but since it was suggested at 15k I decided to do it. Most of my driving is on highways.