Microsoft maintains a dedicated portal for legacy software. You will likely need to sign in with a Microsoft Account (Outlook, Hotmail, etc.) and join the "Visual Studio Dev Essentials" program. This is free and gives you access to the legacy keys and ISOs.
"Why 2015?" his coworker Maya had asked earlier, grimacing. "That’s ancient."
Fix: The old web installer endpoints are slow. Download the instead of the web installer. The ISO is self-contained and does not rely on deprecated Microsoft live feeds.