Is prayer in the mosque valid if the adhan is called two hours before sunrise, and the prayer is performed 15 minutes later, and it remains dark after leaving the mosque, which leads the worshiper to repeat the prayer 54 minutes before sunrise?

The validity of the Fajr prayer depends on the entry of its time with the appearance of the true dawn (al-Fajr al-Sadiq). If the worshipper is certain or predominantly believes that their prayer was performed after the time had begun, then their prayer is valid and they are not required to repeat it. The presence of darkness does not affect the validity of the prayer as long as it is performed after its time has entered. It has been authentically reported that the Prophet, peace and blessings be upon him, used to pray Fajr bi-ghalas (when the light of dawn was mixed with the darkness of night), which indicates the merit of performing the Fajr prayer early in its prescribed time.