That means, the distance betweening the buildings are more likely to be close than that at a big university.
"Betweening" isn't a word. It's the distance between buildings.
Either "the distances between the buildings are more likely to be small" or "the buildings are more likely to be close together."
There is no need for the comma.
Therefore, students who attend a small university can save time becuase the amount of time which takes to move from one class to another class will be samll.
If you spell "because" and "small" correctly the sentence is OK if you add "it" between "which" and "takes."
I do not agree with the theme at all. "Small university" usually refers to the number of students enrolled, not the geographic size. A small university may have a very large campus.
I also don't know that the amount of time saved between classes is significant.