Microsoft does not provide a single ISO file for Visual Studio 2019. Instead, you must create a "local layout" using a command-line tool. This allows you to download all necessary files onto one machine and transfer them to another that has no internet access Stack Overflow Step 1: Download the Bootstrapper
The download speed was still slow, but it didn't matter. He was creating a local cache. A standalone installer that required no internet connection once it was finished. He wasn't fighting the bandwidth; he was beating it by decoupling the process. visual studio 2019 offline installer