Ubuntu Server 14.04 Hyper-V – No Internet

What you're saying doesn't really make sense. The "correct" way to setup networking with Hyper-V is to:

• Connect the one Physical NIC to the MVNS only, nothing else, Hyper-V will configure this for you and there's no reason to mess with it.
• Create a virtual NIC that's connected to one of the virtual switches (or virtual networks as the Hyper-V Manager calls them).

There are three types of Virtual Networks you can create:

• External: connected to the Physical NIC, the Virtual NIC on the Host, and any VMs you assign to it.
• Internal: connected to the Virual NIC on the Host and any VMs you assign it to.
• Private: connected to any VMs you assign it to and nothing else.

The Virtual NIC will always have access to the Physical NIC when configure properly.

If you just want the VMs to have access to just the Hyper-V Host, you can use an Internal. You can also use an External Network and they will have access to the Physical NIC's network.

Since it's a new system, it may have needed to download and install quite a few updated packages. If the slowness is still present, try doing something like

ps -ef|grep apt

on the virtual machine to see if there's an apt-related process running. If the slowness suddenly resolved itself, it's worth checking /var/log/dpkg.log to see if a bunch of packages were installed, causing the slowness.