i have owned a e46 m3 previously before the current e92 N55 and i would change my oil every 10k. it all depends on how you drive. if you go over 5k rpm consistantly, then you should change it every 4-5k miles. the dealer assumes the car has been driven normally thats why they do it every year or 15k. i get my oil and filter changed for 60 bucks. so its not a big hole in my wallet at all. If your in Los Angeles and you dont race every car that comes next to you then changing your oil 9-12k is fine.