Giving significance to the night of 15th Sha'ban, visiting graveyards, doing extra Ibaadah (worship) and offering extra Nawaafil Salaah with the intention of specifically doing so on the occasion of 15th Sha'ban, having illuminations, considering it to be the Eid of the dead and keeping awake for the whole night of 15th Sha'ban and encouraging others to do the same -- all these are Bid'ah (innovation) . The prophet and the Sahaabah never did so nor commanded the muslims to do so.
We don't find any evidence of such things in the entire authentic Seerah of the Prophet and his companions. According to Allamah Ibn Rajab Abu Bakr Turtoshi, Ibn Wazzah Qurtubi, Suyuti, Shokani etc.
