GTA Online is getting a slew of improvements but the loading times are still horrendous so here is the quickest way of getting yourself online, in order to sell those ill-gained goods.
GTA Online is about to receive The Criminal Enterprises update which will enable Sell missions in invite-only sessions. Considering you can already resupply your businesses and trigger heists or their preparations in these sessions, there is a high chance people will play in them exclusively, especially because the loading times are much better than for Public sessions.
One might think that getting into an invite-only session would require you to endure that endless loading screen before entering online but that is actually not the case.
The trick is to get into GTA V singleplayer first instead as it loads much quicker. If you're playing on Steam, you will get a prompt that will ask if you want to go straight to online but you will need to pick the other option instead.
Once you gain control of Michael, Trevor or Franklin, open the menu and navigate to the Online tab. Click Go Online.
After you've done that, just move your selection down to Invite Only Session.
Due to the quick loading times for both singleplayer and invite-only sessions, you will save up a lot as long as you keep dodging public sessions this way.
If you want to increase your loading time further, make sure you're spawning in your apartment, auto shop or some other static location. If you choose "Last Location", the loading time will increase. Kosatka is also not recommended as it spawns at various locations.