Hello Dennis,
thanks for reaching out. CoSpaces requires indeed a quick and stable internet connection in order to work correctly. Just from what you described I don't think that there were issues with our servers because you said that the spaces did load for a few students quickly. But I also don't want to blame your internet connection because of the same reason. So here some general thoughts on how CoSpaces works and maybe we can conclude some tips for next time.
Most data is transferred when you first open a space. The bigger the space is and the more assets it has (images, 360° backgrounds etc.) the more data needs to be transferred, therefore it takes longer. If you close a space and open it again it should load quicker than the first time because most data has already been downloaded. Also, once you're in a space it should work quick as well because most work happens on your computer now and syncing with the server is mostly minimal.
The "Welcome to CoSpaces" space downloads roughly 17 MB. If you open a new empty space it's about 3 MB. So maybe because all 20 students tried to open the "Welcome to CoSpaces" space (which is relatively big in comparison to an empty space) at the same time, it was too much for the internet connection in your classroom and everything slowed down.
What you can try next time is to make sure that not every student is open a new space at the same time. Only first five students, if everything has downloaded the next five students and so on. Once all students have successfully opened the space it should run smooth from there on, assuming you have a stable internet connection.
I'm not one hundred percent sure if this was the problem but we can try. Please let us know if it worked.
Thanks,
Benjamin