I’m not sure if you needed this info or not (because you were specifically asking for help interpreting a reg) but your son will not be able to log PIC until the check ride. So if it takes 8 hours of training to be checkride ready, and 2 hrs for the ride itself, he will start with 10hrs multi, of that, 2hrs being PIC. Add 15hrs PIC after that and then there’s 25 hrs in a multi that is required for a regional and 15 PIC to add an MEI. Now, he can log PIC time while prepping for the MEI ride with an instructor so there is no need to log that 15 PIC first before starting MEI training.