What is a typical teaching load? Are four 3-credit classes a typical burden for full-time faculty? Assume all are in-person courses, no new preps, no new books, no TAs, 15-25 students per class, no research/publishing required, and committee work is required.
It's probably reasonable.  The teaching load for a full-time lecturer with no research responsibility tends to range between 10 and 15 units, equal to two or three 5-unit lecture courses, perhaps one more if some are 3-unit.  What constitutes a full-time load at any given school is largely dictated by the financial reality imposed by their average class size and, thus, the tuition revenue per course from which you and all the other expenses must be paid.  If their class sizes are really small, as they are at your school, they pretty much have to load up each instructor to make it work.