I'm a teacher and I pump at school. It's not an optimal situation, but I am now pumping in the men's staff bathroom (it doesn't get used as much as the women's bathroom so I have less of a chance of being interrupted by someone knocking on the door). I teach kindergarten and have a classroom aide, so she handles a bathroom break/worksheet time for the kids while I go pump for 10 minutes. I am only working in the mornings, so I only have to pump once/day. I'm not gonna lie. It sucks...royally...but, it is completely, 100% worth it in the end.
My schedule looks like this:
6:30-6:45 feed baby on one side and pump on the other at home before I leave for school
9:30 - 9:40 pump in the bathroom at school
10:15 - 11:00 specials class (sometimes I can go pump a little more during this time if I didn't really get the full 10 minutes earlier)
11:00 -11:30 lunch for kids and I go home
11:40 nurse my baby at home!
Is there someone that could cover your class for 15 minutes while you went somewhere to pump? If kindergarten kids can work independently-ish for 15 minutes, anybody can!