Strange, by the time the 915 came out the magazines were all stainless as I recall.
The blue ones were phased out to stainless and still were only 14 rounders with black followers, like the 659's.
Later came the all stainless 15 rounders with the orange followers for the 915 and 5906, etc.
I never saw a S&W 15 rounder in blue, factory, unless I missed something.
No idea what CDNN has.
That said, I do have some factory 20s made for the original model 59 in blue.
I did have a 915 that kept all shots in a playing card over 25 yards, stupid me sold it.
$350 is not out of line for a low mile example with the B&P, seeing some with wear for $400 firm.