Not disagree-ing with your points, but do you have a source for this? It doesn't pass the sniff test to me.
1.5B people is ~ 20% of the world population, and probably closer to 50% of those with computers & internet capable of downloading reddit.com, an image heavy forum.
I'm in the demographic for Reddit (30s, male, western country), and I think maybe 10% of my friends, family & coworkers even know what Reddit is, let along are an MAU.
