Well, Ford UK recommends 12 month 12,500 mile OCIs as standard on all new Fords in England. I don't know what oil and filter they are using as standard. A lot of the Fords sold over there are the same as the Fords sold here. In Europe they've been extending drains for years. I'd say a lot depends on the car. For example, if your mfg. says a standard OCI is 7500, I would think 15K is perfectly possible using a full synthetic oil and a quality filter like a PureOne, Bosch Distance, or a Fram Extended Guard. It also depends on your use. Long runs and easy driving help to extend your OCI.