When connected to a VPN (Virtual Private Network) service, any speed test is measuring the entire pipeline of connectivity, which looks like this:
Browser->VPN process on PC->Router->ISP infrastructure->Internet Backbone->VPN provider Server->Internet backbone->ISP infrastructure->Target Test server(s)
In that chain, neither the VPN Process nor the VPN service perform sufficient (or often, any) traffic control to mitigate latencies. If anything, the process on the PC adds latencies at origin due to the time it takes to encrypt the packets.
So even though the IQrouter is managing the latencies of the streams in and out of the router, it can not influence the end-to-end latencies of a VPN tunnel. What it does do is ensure none of the encrypted packets are lost or delayed due to BufferBloat between the router and the VPN service, and helps keep the tunnel up longer and running smoother than a line with BufferBloat would.
Speed (or capacity) is impacted because your traffic is competing with hundreds (if not thousands) of others at the ingress/egress of the VPN service, as well as the overhead of encryption/decryption.
Also, since the type and class of traffic (e.g. VoIP vs bulk file transfer) the PC is doing is hidden by the VPN Tunnel, the IQrouter traffic manager is not able to prioritize small, frequent and regular payloads for VoIP vs the the larger payloads of the file transfer. So some of the benefits of the IQrouter are lost when traffic is 'hidden' in the VPN tunnel.
So the best answer to mitigate this is to find a VPN provider that actively works to minimize latencies through the tunnel.
Sorry, we don't have any recommendations at this time.