I skipped the 15k, my dealer wanted to charge me $230! Basically they change your oil, check your fluids, possibly top your antifreeze, rotate your tires, lube somethings here and there, and something else... for $230, I said no thanks!
Basically they stick their finger in your butt and wiggle it around.
I skipped mine too. Or rather, I performed it myself.
I just checked on mysubaru.com:
replace engine oil
replace engine oil filter
inspect disc brake pads and discs, axle boots and axle shaft joint portions
inspect brake lines, check operation of parking and service brake system
inspect clutch operation
inspect steering and suspension
And that's it.
Spark plugs are supposed to be good for 30K miles, but if you've still got the factory Champion plugs in there, yank them NOW! Put the NGK copper plugs in and change them every 15k or so. I do and it makes my car happy.
Bummer - it's time to balance and rotate my tires again. That means I need to go out and pull the weights off and take it in. The shop screwed me, so I'm getting my 5000 mile balance and rotations done just like the receipt says I can. free.
That and it's been 10k miles since I cleaned my air filter. Hmm. Do I want to clean it again? Do I?