The Salafi denies the validity of the Masnoon fast of the 15th.

Answer

Yes, it is Sunnah. The Salafi is a moron. All the great Auliya in every century fasted on this Day. Whilst fasting on the 13th, 14th and 15th of every Islamic month is Sunnah, the 15th Day of Sha'baan has special significance since it was specifically ordered by Rasulullah (Sallallahu alayhi wasallam). Those with weak (Dhaeef) brains claim that the narration is fabricated. They are too stupid to understand what is mawdhoo', dhaeef, saheeh, etc.