Here are some steps to improve your internet connection when you are connected to a VPN:
Check your internet connection.
Disable Wi-Fi, if possible.
Connect devices to the VPN using a wired connection.
Check your VPN’s obfuscation status.
Adjust the encryption settings and/or protocols used for your VPN connection.
Check if your VPN network supports bridge (split) tunneling.
Disable local overloading/compression.
Change your security settings.