Which of the following was not a cause of popular dissatisfaction with the Roman Catholic Church in the early 15th century?
fiscal practices of the papacy, moral laxity of the clergy, the failure of the church to meet spiritual needs, increasing austerity and the use of the vernacular within the church, the papacy's secular intrests
The one that jumps out to me is the increasing austerity and the use of vernacular within the church. Given that so much of the objections to the church, take Martin Luthers, were based around the other practices like the selling of indulgences and the moral laxity of the clergy that one almost assumes that the answer has to be the increased use of vernacular.
One of the changes that actually appealed to people was this use of vernacular as it allowed them to understand the mass which they'd never really been able to understand before. Particularly since the Bible had been translated into the vernacular, this move was wildly popular with lay people as it allowed them further insight into religion which previously had only been the exclusive right of the clergy.