Since a VPN usually pipes all your connections through a single IP and more (no need to discuss how a VPN works here) then it's easier to throttle as well as see speed issues as all content goes through the VPN.
The reason to use a VPN should be for what a VPN is good for, not this.
Be sure and test this as it's been widely discussed as in "I installed a VPN, it's slower, why?"
I have been told that a vpv can stop your ip from throttling your speeds. Dose this mean i could select a cheaper plan but still get the higher speeds