Q: Is there anything I should be doing during the 15th night of Shaʿbān
A: The Prophet (peace be upon him) said, “During the middle night of Shaʿbān
And so, the middle night of Shaʿbān contains a great deal of virtue. Some from the pious sages of the past would pray during that night.
This night is one of the few in which praying and staying awake for its entirety for worship is recommended.
It should be noted, however, gathering in the masjids for worship along with such prayers known as ṣalāt al-raghāʾib and al-alfiyyah are innovations.
Source: Sunan Ibn Majah, Sharh al-Muntaha & Kash-shaf