They analyze internet packets, detect VPN connections and deliberately throttle them.
They just slow down anything that is not a common protocol (not http, https, ftp, …) that would make other things like torrent or even ssh session to be also equally slow.
If it is the first possibility, I know that OpenVPN with static key tend to be very difficult to detect if not impossible. Its also a bit faster but it has its cons that I encourage you to read about.
If it is the second possibility then you need to disguise your VPN traffic as https. I know its doable but I am fuzzy on the details.
Regarding VPN being slow, two possibilities here:
If it is the first possibility, I know that OpenVPN with static key tend to be very difficult to detect if not impossible. Its also a bit faster but it has its cons that I encourage you to read about.
If it is the second possibility then you need to disguise your VPN traffic as https. I know its doable but I am fuzzy on the details.