praise be to allah, the lord of the world; and blessings and peace be upon our prophet muhammad and upon all his family and companions.

the actions of people are presented to allah in the month of shaban so the prophet (salla allahu alaihi wa sallam) used to fast repeatedly in this month aisha () said: "i never saw the messenger of allah fast for a complete month except for ramadhan, and i never saw him do more fasting in any month than he did in shaban". [reported by bukhari and muslim]

usamah bin zaid reported "i said to the prophet, o messenger of allah! i did not see you fasting in any month as you do in the month of shaban". the prophet said: "people neglect this month which is between rajab and ramadhan, in this month the actions of the people are presented to allah; so i like my deeds to be presented while i am fasting". [abu dawood, al-nasaie]

as for fasting particularly the fifteenth of shaban this is not proved through any sound evidence.
there are some sayings of the companions of the prophet and their immediate followers which indicate the virtue of this night. but this does not mean that there is any special significance to the day or that night. so, there is no evidence proving that fasting such a day is sunnah nor is there any evidence proving that there are some specific prayers to be performed on shaban night (15).