at 15K you shouldn't see hardly any wear that means much of anything regarding how they will work out over time.
I'm at 42K and have a little more than 50% of the pad left on both fronts and rears. The type of brake use can change the difference between rears vs fronts wearing faster etc. Lots of very light bleeding off of speed brake use you might actually see the rear pads wearing more than the fronts. More standard braking use stop signs etc where heavier use of the brake is involved the front pads for sure will show faster rate of wear than the rears. I have found this to be the case on all my cars AWD or two wheel drive.
As for subaru they historically have used very good rotors and long lasting pads even with fairly heavy use I expect to see 65,000 miles on my stock pads.
The one odd thing I did notice was between about 35,000 miles and 40,000 miles the pads developed a nasty grind noise when the brakes were used under light stopping for a period of several days. However once the car was run at higher speeds and the brakes were used for heavier longer stops the grinding went away. I checked all the pads twice given the grinding sound was pretty terrible sounding. Now at just over 42,000 miles the grinding has abated and they are quiet and smooth like they were prior to the mid to late 30K range. Starting to think that the pads had a slight change in material hardness or make up and now that they have been worn down a little more that spot in the pads is gone and I'm back to the same type of pad material the pads had earlier on.
Either way for sure the pads are all 100% fine regarding life but something was a little goofy about the material on the pads for a few thousand miles.
I can easily see a dealer selling a car owner new brakes and rotors when they heard the grind sound I was getting. Heck without actually looking my self I would have thought something major was up with the brakes. As it turned out they were perfectly fine but the pads were for sure picking up either dust or had something different in the material causing the grind sound.