a brand new server slowing down the network?

I work in a small/medium-sized network environment with about 150 users. I recently set up a Windows Server 2016 with Hyper-V role on a brand new tower that we were not using. It's housing 3 Hyper-V Ubuntu Apache VMs. They are connected to a virtual internal NAT switch.

I was setting up an open source ticketing system on one of the VMs (2 other Apache servers were not running at the time). We started receiving phone calls from people that the internet was very slow. I noticed that the timing coincided with the time when I turned on the server and working on the server. The internet speed came back to normal when I shut down the Windows Server.

I am gonna go back to work and find out what's taking up network resources the most from the server. What could possibly be causing the network congestion?