Internet problems, high latency and high jitter

Hi,

I am troubleshooting a network and looking for advice.

The network has 1 physical server with 2 VMs. There are about 38 clients on the network. It is a Windows based network. They are currently using a 12Mbps down x 2Mbps up internet line. They primarily use all web applications including a remote desktop app, which most users are logged into all the time.

- They have recently started really having major issues with internet. It's very slow, mostly noticeable within the rdp sessions.
- When running speed tests at the high of the day, I pretty regularly can report speeds of 12Mbps/1Mbps
- When running speed tests at night with no users, I get about the same speeds
- I have have the ISP test the line, they see high latency
- When I do broadband quality tests, I also see the latency issues, jitter is usually between 30ms and 80ms
- When I try to upload a 500meg file it completely chokes the internet, it just stops working.

I already know that they are over utilizing their current internet line, but what is confusing me is that they were using a T1 line when I came in, and I got them to upgrade (which was like pulling teeth), it was always slow before, it got better with the upgrade, but still fairly slow. But in the last 2 months, it has gotten terrible.

I am unable to do a traceroute to see where the latency starts. I am assuming because they use a vpn, but I don't have any control over the vpn settings at this point.

My next step is to go onsite after hours, disconnect everything from the network and test with the ISP, and slowly add computers back to the network to see when the problems start.

Any ideas of what I can test, or where I should be looking?

Any help is appreciated.

Thanks