We recommend 15 as not to overwhelm Campus. This is what Campus itself will configure on the devices by default. Of course, if you don't have many switches and/or you don't have extremely frequent changes, then you can shorten this. I have a feeling, though, that a university would tend to generate more notifications than most organizations. Therefore, test various values for this number to find a balance between update time, CPU load, and until updates start being dropped.