Because of the very long service intervals on the car the dealer is bound to take the cautious approach to brake pad replacement as he's not going to see the car for another 15,000 miles or maybe even more
Consequently, it's probably fair to assume that they won't last for another 15,000 miles...
Based on 4 months of motorway driving personally I'd keep the existing pads and keep an eye on them, but this one's got to be up to you...
Tigger.