I'm sure BMW is aware that 15K is not a safe oil chnage interval, but all they care about ti to get you to the end of your warranty period. After that its not their problem. I still think the main reason they have a 15K interval is because they are the ones having to pay for it under their "free maintenace program". From what I remember, the Audi RS4 is 10K even though it uses similar oil and is NA. Other Audi's are also 10K. Lexus IS's have shorter intervals too, all because its not covered under a "free maintenance program."
jet black 335i, 6MT manual, black interior with silver aluminum trim, PP, SP.