“I see one big problem with 15K oil change intervals. Many guys don’t check their oil level at all in between oil changes. Suppose with a 5K interval, the engine is 1 quart down by the time 5K has elapsed. With a 15K interval, the engine might be 3 quarts down. And what if the engine crankcase only holds 4 quarts? No, no . . . 15K is not a good idea.”
That is exactly the point that I made in my comment on page 2 of this thread.
I’m glad to see that you agree with me.