Context: Persia attempted to ratify the Treaty of Constantinople , by demanding that the Ja'fari, also known as the Imamiyyah was to be accepted as a fifth legal sect of Islam. In 1743, Nader Shah declared war on the Ottoman Empire. He demanded the surrender of Baghdad. The Persians had captured Baghdad in 1623 and Mosul in 1624, but the Ottomans had recaptured Mosul in 1625 and Bagdad in 1638. The Treaty of Zuhab in 1639 between the Ottoman Empire and the Safavid Empire had resulted in peace for 85 years. After the fall of the Safavid Dynasty, Russia and the Ottoman Empire agreed to divide the northwest and the Caspian region of Persia, but with the advent of Nader Shah, the Russians and the Turks withdrew from the region. Nader Shah waged war against the Ottomans from 1730 to 1736 but it ended with a stalemate. Nader Shah afterwards turned east and declared war on the Moghul Empire and invaded India, in order to refund his wars against the Ottomans.

Question: How many years did the Persians rule over Baghdad before the Ottomans recaptured the town?

Answer:
15