It doesn't explain some things to me. Maybe I read the article inattentively, but which stage of the loading hangs for a very long time? Loading screen, or city overview when joining a session? In my experience, on modern hardware, the loading screen goes very quickly (a minute or two).
What's worth noting is that the city overview can hang for 20-30 minutes during connecting. At the same time, suspending the GTAV.exe for 20-30 seconds allows you to immediately throw the player into an empty public session. It is unlikely caused by slow parsing of json, more like the suspend causes udp timeout when connecting to the slow session hosts.