What is the ruling on delaying prayer by fifteen minutes past its time?

Preserving the performance of prayer at its appointed time is one of the best righteous deeds, as stated in the Hadith: "Prayer at its appointed time." Allah has forbidden negligence and dereliction concerning prayer, as He says: "There succeeded them a later generation who neglected prayers and pursued desires; so they are going to meet evil." Delaying prayer beyond its appointed time without a legitimate Shar'i excuse is a great sin, necessitating immediate repentance and performance of the prayer, for the Prophet, peace and blessings be upon him, said: "Whoever forgets a prayer, let him pray it when he remembers it, for there is no expiation for it other than that."