All VPNs are going to somewhat slow the speed of your connection to any site because that is how the system works and it requires firstly a greater amount of data transfer from point to point and it requires the computing effort of deciphering the encrypted point to point messaging.
Sites have to have the right resources to accept VPN traffic and somehow understand this is more expensive and has to make business sense.
Is this true? Because according to some IT experts, using VPN can also significantly increase internet connection speed when the internet is interrupted. I myself have experienced this situation many times whenever the internet in my country has problems. I have used VPN like Express, and Nord and connected to recommended servers and it gives a better browsing experience. I have not tried using VPN for gambling sites but I have found that VPN does not always slow down our connection.
Also, I think the VPN service we choose will also affect the internet speed.