Gentleman, there is no way getting around it... new oil is better than old oil at lubrication, partly due to heat breakdown, and partly due to the detergents getting spent and the suspension capability of the oil degrading. Sure it will meet the minimum spec of the manufacturer if kept in the crank case for 15000 miles, but what about 15001? Are we to believe that magically the oil goes from perfectly suitable to unacceptable in one mile? Think for yourself and don't let others think for you.

So clearly there is SOME benefit to having newer oil in the crankcase.. And I'm sorry, but a one size fits all 15000 interval is meaningless.. I live in Phoenix where it's extremely hot and there is a lot of idling of engines in extreme heat.. This is in contrast to someone who might live in a much cooler (but not frozen) climate, and yet again we're both in contrast to someone living in a sub zero climate.. some of us might drive mostly long freeway trips and others might do stop and go all day long..

If you are leasing your car and couldn't care less about how long it lasts after your 36000 or what ever miles.. do what BMW says. BMW (and all other makers) have to balance the economics of maintenance costs with the life of the car. If they told you to do everything possible to keep it running well for 250,000 then it would cost too much to own for some and they'd loose sales. They know that most 100,000 cars wind up on the 3rd world market or other sub market where the buyers don't get involved in new car buying decisions and have little effect on reliability ratings so they don't really care. I however will own a vehicle for 150,000+ miles before I personally sell it off, and I want it to be trouble free for all of those miles!

Nuff said.. do what you want, and I'll do what I want.

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BMW - X5 4.8i w/all US options packages, 19" Y wheels, White/Tobacco, Huper Optik 50% tint
Mercedes Benz - E320 CDI Park Assist, NAV, Folding Mirrors, Premium Sound, Voice Command, Sunroof, Auto Rear Shade, Bi-Xenon