reddits true size lies at around 5 million or less. Less than 5 times Lemmy’s size.
Lemmy doesn’t have 1.5 million active users; that’s how many active users the Fediverse as a whole has; most of those are Mastodon users. Lemmy has around 32K active users. So if your 5 million number is right, Reddit is around 156 times larger than us.