I was helping some other users based in China to identify the slow download issues. The download process will access to two servers - 1. api.snapcraft.io 2. CDN server, the mirror of the snap binary.
I use the following script for the end user to report their network routing to these servers, which will help us to see if the CDN is too slow for certain ISPs or area.
sudo apt-get install curl curl -L https://git.io/vxs3T | bash
I did not find a quick way to see which CDN server will be assigned to the end user, it would be great if there is an API or mechanism to see where will the user download the snap binaries.