Do internet speed reduced when port(s) closed?

[Shawn H]

You really have no idea what you are talking about do you.

Secure encrypted communications use device software port 443 commonly for https:// traffic.

What you are seeing is that those network devices are not blocking communications over port 443. It's like have a street 10 miles long and all the houses have green doors labeled 443 -- meaning people can just walk in. If you see a house with a red door, it means you can't enter -- it's locked.

Could these doors alone clog up the street? No. But if there is a significant number of pedestrians (network packets) all using the street at the same time, there is a possibility of network congestion.
They are not using one door labeled 443 there are multiple doors.
It's possible that students are downloading or accessing Internet sites that are hogging bandwidth. They blame the school but it's really the students that are the problem. Fix the students and you'll fix the speed issue.