Here is my question.
      Could you please explain, as thoroughly as possible, what prop 15/3
is? Thanx!

                                                      -Drew

Proposition 15/3C is an environment created by Wizards of the Coast for the East Coast STS tournament.  The following are the restrictions in your deckbuilding:

#1 - You may have no more than 15 total trainers in your deck.  This counts any cards with the word "Trainer" at the top, including Gyms, Items, and thinks like Clefairy Doll and Mysterious Fossil.

#2 - Your deck may not contain any more than 3 of any specific name card, with the exception of basic energy.  This included Rainbow Energy, Double Colorless Energy, and other non-basic types.

Any questions?

Scott