i wouldn't doubt that the first tires aren't rated to last long.
my parents have used the same service advisor at the same lexus dealership for over a decade. even he tells us to get better tires (like michelin) and not use what was put on originally.
periodically, they have sales at the dealership, but they're still crackhead prices. i purchased 4 michelin tires for my expedition from ntb (when they were still owned by sears) that were priced at 950.00 for 745.00 after showing them the prices at discount tire. i got at least 50k out of those tires, but that's what they were rated for.
lexus wanted about the same amount 989.00 for michelins that would fit my rx. given that my expedition used all terrain suv tires that were not rated for smooth driving, perhaps the touring tires will wear out easier.
still, 15k is not very good for new tires, imo.