The bandwidth used will vary depending on:

- the graphical content, 

- colors

- peripheral redirection 

- streaming content and uploading / downloading files and printing. 

You will be able to pin down which application is using the most bandwidth by using Microsoft resource monitor.

In short, a remote session will use between 20kbps to 100kbps. 

To solve your performance issue, you can either ask your virtual machine host to add an extra network adapter card for your server (if that option is available) or do the following to tweak your server for better performances :

  • Disable background & animation for better performance in the general tab of the client generator.
  • Choose 15 bits color display in the display tab of the client generator.  
  • Make sure your application does not display animated items such as .gif or videos. These are known to enhance greatly the bandwidth used.  
  • Prevent device redirection and sound, only local disks are needed to be redirected if you need to print using the Universal Printer.  
  • If your users have a full remote desktop displayed, force the classic desktop them by group policy, this can be done here :
  • Disable peek on windows 10/2016 by editing system properties / advanced / performance