Changing it earlier can't hurt the car, whereas changing it too late definitely can.
It's a question of BMW trying to save money on their free maintenance vs shops trying to make more money by telling people to change oil earlier.
If you plan on keeping your car for the long haul, IMO it's better to err on the side of more frequent oil changes to protect the engine better. 15k miles on oil is a really long time...7500 miles is a happy medium. Even 5000 miles is a little soon on synthetic oil.
AW/Terra | ZSP | ZPP | ZCW | iDrive | CA
Mods: BC BR coilovers | Blacklines | M-tech rear | dual exhaust | M3 steering wheel | BMW SSK | ZHP shift knob | High-kick CF spoiler | NBT Retrofit
M3 front control arms | M3 rear guide rods | Manzo rear toe and camber links | Monroe rear shock mounts | Varrstoen ES1 19x9.5+20 Front, 19x11+25 rear