Primers are not necessarily indicators of excessive pressure unless totally "Nailed" or blown primer pockets, and "nailed could be excessive head space.

OPs orig pictures ARE NOT FLAT flat primers.

15.0gr of 2400 under a 158gr bullet (unless a full wadcutter or maybe w/mag primer) is not going to be a problem in any .357 Magnum rated revolver.

Nosler manual for handgun ammo is an outlier -- if you don't believe, compare .44 Mag and .454 Casul to other manuals.

FWIW,

Paul