[GrnMchin]

15k between oil changes seem way to long. The oil lubricating properties may not break down, but the oil would be filled with metal by then and cause a lot more wear. I used Mobil 1 and Red Line in the past with a truck I used for heavy towing (14K +) and went well over 100k before selling for a new one and never had any engine failures. If you go say 6k between oil changes then at least change your filter every 3k with a high quality filter.