Just remember to stock up on the Wilson as who knows when they will switch to BT7. I can't imagine Babolat keeping two process for gut going just for Wilson and Prince.
I find 17 gauge VS to be more comfortable, a tad more spin and power than 16 gauge. As far as durability, you get about 10% more from using 16 gauge and probably 20% more using 15g but I wouldn't bother with that. Unless you break strings like crazy, I would stick with 17gauge.
If I had to use 15gauge VS, I might as well just use X1 17g instead.