Between the 15 and the 16 for skinning, is a tough call, I just got a 16 a month ago... and am holding off on a 15 till after the holidays... don't think I've been good enough

Anyway, I'm a wrist skinner... one of the reasons I like a drop point over a clip point, the curve of the 16's blade is very good for skinning, but I'd be choking up on the blade, and only using about 2" of sharpened edge. The 15's curve is larger, but of greater radius, so how good it would be for skinning sort of depends on how you prefer to hold and work the blade while you're skinning. For some people (me) the 16 is better, for others, the 15 would give you a lot more edge to work with, so it should stay sharp longer.
Steel, blade geometry, heat treating, and edge style and angle all combine to determine how long your edge will last, especially while skinning. Google "buffalo skinning knife set" sometime and see how much sharpening those guys did while skinning, they worked in teams with 2 or 3 skinners per bison, probably skinning at least 25 a day, I wonder how many times they'd hone their edges per critter. I've read that the limiting factor to how successful, i.e. how much money the buffalo runners were, was how quickly they could skin them, they were paid for the pelts (and tongues), they would only shoot what they could skin, so the faster they could skin, the more money they made.
One of the best knives I've got for skinning is made of 440C, I've had it for going on 30 years now. It's a very small blade, smaller than the 2" curve I'd use on the 16, and I have no trouble getting through 2 elk without sharpening it, course I think your pigs would be harder on the edge. That said, I've had really good luck with Knives of Alaska D2 steel. Haven't followed their prices, I bought mine when they first came out, and they were a very good value (relatively inexpensive for the quality). I've noticed that its a lot easier to sharpen the Becker 1095 steel than my D2 blades, I haven't really used them hard enough to judge if they'll hold an edge as long as D2, my guess is they won't, but I tend to dress my edges with a strop pretty regularly, so they never really get dull.
I'm guessing that no matter what steel you end up with, and no matter what blade design you choose, you'll probably find that you need to sharpen/maintain your edge while skinning. Remember, the whole goal of skinning is to remove the skin without contaminating the carcass, the sharper your knife is, the easier the job will be. If I knew I was going to have to skin in the field, I'd carry a way to touch up and maintain my edge.
Erik