Hello asyvret!
First of all, we apologize for taking so long to reply. It looks like your post went under our radar for some reason.
Videotron does not throttle its Internet connections based on protocol or type of usage (this incluees VPN, bittorent, streaming, etc).
If your speed is what it should be when not using the VPN, we recommend contacting your VPN's administrator for assistance. There are multiple possible causes for low speed when using a VPN or Proxy, including routing, software issue, antivirus/firewall, server issue, etc.
We hope this helps!
-JFrancoisD