How did religious life change from the 15th to the 16th centuries?
The main change in European religious life in this period was the rise of Protestantism, or the "Protestant Reformation." The corresponding reform of Roman Catholicism, culminating in the Council of Trent (or "Tridentine reforms") which happened slightly later, was known as the "counter-Reformation.
The Protestant Reformation was a series of theological and ecclesiastical movements within Christianity, of which one of the most important moments was the promulgation of Martin Luther's 95 Theses in 1517 (not nailed to the door of the Wittenberg Cathedral, as in popular myth, but properly presented for disputation at the university).
Protestantism, as articulated by Luther, Calvin, Zwingli, and other major reformation thinkers differed from Roman Catholicism in having services in the vernacular, encouraging the laity to read vernacular translations of the Bible for themselves, giving communion in both kinds (bread and wine) to both clergy and laity, ending indulgences, and minimizing the role of saints. The new Protestant groups had decentralized power (no single Pope), minimized divisions between clergy and laity ("priesthood of all believers"), emphasized Bible reading and faith as paths to salvation as apposed to extreme sacramentalism ("sola scriptura", "salvation by faith"), and generally abolished monasticism.