Seminary is not just studies, otherwise it would be called college.
The spiritual and pastoral formation is mainly out of the classroom and varies a lot by diocese or community. For instance, as a Legionary, I went out and ran youth clubs for 4 years between philosophy and theology.
As far as studies, theology in Rome is only three years but it is intense (20 credit hours most semesters).
As far as math, literature, and things beyond pastoral, philosophy, and theology. Think of the souls you are called to save! A priest needs to have at least a basic grasp of other things to reach souls.
Studies can vary in religious communities: for instance we do an AA (I think the title is religious studies and classical humanities) over a two year novitiate and one year of humanities, then we do an intense two-year philosophy program. However, few communities have the resources to do this all in-house like we do.
Going to seminary is giving your time to God, so one needs to give generously.