Ok, I just did 20 load tests… With an empty community folder, my game on my system with an NVME SSD and 32 gigs of ram loads the game from the first click to the main menu in 110 sec. Just adding a basic airport add-on with some textures from Google Earth adds 7 sec to the loading time. Adding a big add-on like the monument valley will add an additional 37 sec to the loading time.
Adding 600 liveries only ads 27 sec to the loading time.
In total, my loading time with about 15 scenery ads ods and 600 liveries ads 90 sec to the game loading time for me.
This is just to let you know that almost anything you add in your community folder has some impact on loading time. But airports and additional objects have a much bigger impact than liveries, and that is logical because the airports have to be loaded in the world map.
This is just for information sake only, and your performance may be very different than mine.