If you have a lot of users on at the same time obviously your connection speed is going to drop. Not much you can do about it, except maybe wait until midnight for everyone to go to bed.
But what if you don't know if it is overcrowding, trouble at the tower, poor signal reception, or incorrect computer settings? Anyway to tell?
There is a data field in your debug screen labeled "Ec/Io" (not all connection managers show this data):
Once you have your antenna positioned to receive the best signal you can via the signal strength meter (and you didn't do this at the busiest time of the day for tower traffic) you can have a baseline number for Ec/Io. That is, you will have a dB range that is normal for your connection speed and signal. Any variation of this baseline will give you a clue something is not optimal. A crowded tower is one of them.
So if your Ec/Io number is down there around -3.0 or lower, you pretty much have a sector of the tower to yourself. But keep in mind you need some kind of baseline number to compare it to. If you have great speeds and low latency take a look at your debug screen and that number. Make that your baseline.
There are of course other things that can effect Ec/Io, such as pilot pollution (overlapping sector signals), but too many people on at once is certainly a culprit that will raise that number.