I have been doing it every 7,500 cause 15,000 is way to extreme. I have independant shops change it in between, and don't reset the service indicator. I have had 3 oil changes done in 27,000 miles the last one done in conjunction with intake port cleaning.
I have had most major service done at half the interval stated by BMW. Did the plugs at 25,000. Recently did the intake ports, and now thinking its time to flush the coolant.
JB4, BMW Perf. Exhaust, DCI, Strut Brace, KW Series 1, Quaife LSD, Black Kidneys.