What Is Meant by the Blessed Night in Surat Al-Dukhan?
Question

what is the importance of 15 shaban,is it the night in which the fate of every one is decided for the next year?
 
the especial night mentioned in surah Dakan means which night.is it the shaban or Qadar?
Praise be to Allah.Laylat al-Nusf min Sha’baan (the 15th of Sha’baan) is like any other night, and there is no sound report from the Prophet (peace and blessings of Allah be upon him) to indicate that on this night the fate or destiny of people is decided.
See Question no. 8907 .
With regard to the night mentioned in the verses:
“We sent it (this Quran) down on a blessed night. Verily, We are ever warning [mankind that Our Torment will reach those who disbelieve in Our Oneness of Lordship and in Our Oneness of worship].
Therein (that night) is decreed every matter of ordainments”[al-Dukhaan 44:3-4]
Ibn Jareer al-Tabari (may Allah have mercy on him) said: the commentators differed concerning that night, i.e., which night of the year it is. Some of them said that it is Laylat al-Qadr, and it was narrated from Qurtaadah that it is Laylat al-Qadr. Others said that it is the night of the 15th of Sha’baan. The correct view is the view of those who say that it is Laylat al-Qadr, because Allah has told us of that when He says, ‘Verily, We are ever warning’ [al-Dukhaan 44:3].”
(Tafseer al-Tabari, 11/221)
With regard to the phrase, “Therein (that night) is decreed every matter of ordainments”: Ibn Hajar said in his commentary on Saheeh al-Bukhaari: “What this means is that the decrees for the year are decided on that night, because Allah says: ‘Therein (that night) is decreed every matter of ordainments’. And al-Nawawi said: the scholars said that it is called Laylat al-Qadr because on this night the angels write down the decrees (aqdaar), because Allah says, ‘Therein (that night) is decreed every matter of ordainments’. This was also narrated by ‘Abd al-Razzaaq and other mufassireen with saheeh isnaads from Mujaahid, ‘Ikrimah, Qutaadah and others. Al-Toorbashti said that the word used in the Quran is qadr, whereas people think it is qadar (decree); the word qadr refers to the detailed manifestation of the decree.
Laylat al-Qadr brings great reward for the one who does good deeds and strives in worship on that night.
Allah says (interpretation of the meaning):
“Verily, We have sent it (this Quran) down in the Night of Al‑Qadr (Decree). 
And what will make you know what the Night of Al‑Qadr (Decree) is?
The Night of Al‑Qadr (Decree) is better than a thousand months (i.e. worshipping Allah in that night is better than worshipping Him a thousand months, i.e. 83 years and 4 months).
Therein descend the angels and the Rooh [Jibreel (Gabriel)] by Allah’s Permission with all Decrees, 
(All that night), there is peace (and goodness from Allah to His believing slaves) until the appearance of dawn”[al-Qadr 97:1-5]
There are many ahaadeeth which speak of the virtue of that night, such as the hadeeth narrated by al-Bukhaari from Abu Hurayrah, in which the Prophet (peace and blessings of Allah be upon him) said: “Whoever spends Laylat al-Qadr in prayer out of faith and hoping for reward, all his previous sins will be forgiven, and whoever fasts Ramadan out of faith and hoping for reward, all his previous sins will be forgiven.” (Narrated by al-Bukhari, al-Sawm, 1768).
And Allah knows best.