Hi there;
ProGet is quite optimized as a far as software goes (check out ProGet Case Studies to see the scale that enterprises use it at), and a lot of our users have switched from competitive tools for massive performance gains that our tools have. But you need to put it on proper hardware.
Keep in mind that NuGet tools were designed to operate against NuGet.org, which is run on a massive server farm that sends primarily static content. You are making 1000's of requests, and each request to ProGet is comparatively expensive, because it proxies those requests to NuGet.org (assuming you have a connector loaded), makes database connections, it checks permissions, vulnerabilities, etc.
Each request to the server can result in several subsequent network requests... and it sounds like your ProGet server is a Win10 desktop... there's just no way it's going to keep up with developers hammering it with more powerful workstations.
Check out ProGet Free to ProGet Enterprise to see the performance recommendations we have, and other reasons organizations upgrade.