I am a mechanic and I don't believe that an oil change every 15000 Miles is adequate. I change the oil in my M3 every 5000 Miles or before I store the car for the winter, which ever comes first.
2011 E90 M3 ZCP - Individual Moonstone/Individual Amarone Extended/Individual Piano Black With Inlay:LINK!!!
1994 Euro E36 M3 Sedan - Daytona Violet/Mulberry:LINK!!!