Is it possible to watch light of night of decree at 15th of Sha'baan? What is the significance of witnessing such a light?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

We do not know any evidence which proves that one of the signs of the night of Al-Qadr (lofty night during which matters are decreed) is the sighting of a light before, during or after Ramadan. What is reported about the signs of the night Al-Qadr is the saying of the Prophet : "The sign of the night of Al-Qadr is that it is bright and shining, as if there is in it a bright still moon without any cold or wind. The weather during this night is neither hot nor cold. Also, there is no shooting of the stars until the morning. Its sign is that the sun in the morning after this night, rises up without beams exactly like the full moon and Satan does not come out with the sun on this morning."

Lastly, it should be noted that a Muslim should be interested in seeking the reward and obtaining the excellence of the night of Al-Qadr by standing in prayer and reading the Qur'aan during the last ten days of Ramadan.  

Allaah knows best.