There are factory 13 and 15-round mags made specifically for the P30SK/VP9SK. These are the same 13/15-rd mags as the 13-rd USPc/P2000 and 15-rd P30/VP9 mags but the floor plates are different and work better than the x-grips.
Cross Creek Guns (a supporting vendor) has the 15-rounders for $35.50 (part 226346S).
I stick to 10 rounders carry a p30sk AIWB 95% of the time. Other 5% I carry an P30L outside. I use vp9sk 10rd bases or modified p2000sk angled. Like the pinky extension better than the flat from the p30sk (maybe they come with the same now I don't know I bought it early on). A 15 from the L is not THAT much larger than the VP9 but more than an inch longer than a flat p30sk and an inch over angled p2000sk mag. In order.... 10 flat....2000sk....VP9.... 30L 15 round.
That’s a pretty good price. I carry my SK with the flush 10 round mag and keep 2 full size p30 15 rounders for reloads. They work fine, just look a little funny hanging out past the grip. Figure if I need the reload I don’t really care how it looks. Plus they’re interchangeable with the wife’s P30L mags if the need arises.