Your buddy is definately in the ideal situation considering oil life. But IMO, 15000 miles is too long for a blend.
If it was my vehicle, i would be using a top quality synthetic just to be safe. And actually i do; i've got a 08 GMC savanna with the OLM and Amsoil ASL in the sump along with a EAO filter. If you don't want to go Amsoil, at least go with a good synthetic like; PP, Mobil 1 EP, RL, or alike.