Hi
Using a VPN will slow your internet "to some degree" as it reroutes your connection through the VPN server (and encrypts).
The overall speed can also depend on which server(country) you've chosen, distance, time of day (how busy the chosen server is) and integrity of the connection.
So simply put you can expect some slow but typically not an extreme slowing.
Have you tried other 'VPN server locations' offered and is there any difference?