Pope Julius II planned far more for St Peters than Nicholas Vs program of repair or modification. Julius was at that time planning his own tomb, which was to be designed and adorned with sculpture by Michelangelo and placed within St Peters.  In 1505 Julius made a decision to demolish the ancient basilica and replace it with a monumental structure to house his enormous tomb and "aggrandize himself in the popular imagination".  A competition was held, and a number of the designs have survived at the Uffizi Gallery. A succession of popes and architects followed in the next 120 years, their combined efforts resulting in the present building. The scheme begun by Julius II continued through the reigns of Pope Leo X (1513–1521), Pope Hadrian VI (1522–1523). Pope Clement VII (1523–1534), Pope Paul III (1534–1549), Pope Julius III (1550–1555), Pope Marcellus II (1555), Pope Paul IV (1555–1559), Pope Pius IV (1559–1565), Pope Pius V (saint) (1565–1572), Pope Gregory XIII (1572–1585), Pope Sixtus V (1585–1590), Pope Urban VII (1590), Pope Gregory XIV (1590–1591), Pope Innocent IX (1591), Pope Clement VIII (1592–1605), Pope Leo XI (1605), Pope Paul V (1605–1621), Pope Gregory XV (1621–1623), Pope Urban VIII (1623–1644) and Pope Innocent X (1644–1655).
Question: How many more years did Pope Gregory XV reign than Pope Leo XI?
Answer: 1