بسم الله الرحمن الرحيم
You did not send the fatwa of Ibn Baz along with your question. No special deed is proved from Sahih hadith on 15th Shaban. The hadith قوموا ليلها وصوموا نهارها is not Sahih.
Nowadays, people keep themselves awake in this night and offer nafl salah the whole night collectively in the mosque, this is not proved from any Sahih hadith. However, some hadith do speak that it is a night of forgiveness. So if someone seeks the forgiveness from Allah in this night inside his home individually without any celebration, then he may do so. Weak hadith dealing with virtues can be practiced. However, in order to prove Ahkam (Shariah commandments), it is necessary that Sahih hadiths should are available.
Allah knows Best!
Darul Uloom Deoband