2 things...
1. Is the dealer actually rotating them? and If so, are they rotating them in the correct pattern? If you're using quicklane, thats where most service department employees start off. They're the lowest paying and least experienced employees. A lot of times, they're claiming they are rotating and not doing it, or if they are, they're front-rear swapping without crossing. Crossing the front on a RWD based vehicle allows the tires to nibble off the scalloping and edge wear to make the tires wear evenly across the tread. I rotate myself or let discount do it.

2. OEM Dueler tires aren't the best, but 15K is too short. Have you actually put a tread depth gauge on there to measure actual depth? We're all eyballing it through computer monitors, but it looks like you still have 6 or 7/32" left. I would expect at least 40K of life or better.
Other thoughts:
The service writer who called has a job, to sell....and if he can sell you a set of 1500 dollar tires, why not?
Also, most OEM supplied tires do not have any kind of mileage warranty of any sort like retail tires. They do have warranties for manufacturing defects or workmanship issues, but thats it.
Tire applications are funny and complicated .
OEM Manufacturers will negotiate with tire suppliers to purchase bulk amounts of tires, and manufacturers will supply the same models that we can buy from retailers, but meet the OEM requirements for rolling resistance, ride and handling characteristics, (and cost) by changing material compounds etc, or providing an older model tire with lower production costs that still meet the OEMs requirements. Like GM using Goodyear Eagle RS-A, Eagle LS-2, and Wrangler SR-A for the last 30 years on their vehicles. Ford used a Michelin Primacy XC on their 18" F150 offerings, which was generally not sold at retailers, and only an OEM application tire. Ford also used Hankooks for their FX4 package tires and called them "all terrains" and tread life varied wildly on those. Toyota and Lexus loves using soft ass bridgestones on their vehicles that ride great but infuriate owners at 20K when they have cords showing. Some tire manufacturers do supply retail units for OEMs just to get more product out there, I have seen super duty trucks equipped with Michelin LTX MS2 that will get 50-70K.