Don't know if it's related to this pack, but I'm using a pack that is 1.5 GB compressed, 1.9 GB uncompressed. (The link in the OP is a pack that's 1.1 GB, for reference)
It's called "All-in-one v2.9". I tried running it through PNGGauntlet, but it looks like the files have already been optimized.
I actually came here looking to expand on my collection, but it seems like this one was included in the pack I'm using. But sadly, I don't know where the pack I'm using came from, since it was given to me directly from a friend. I went looking for it briefly, but didn't have any luck. Maybe you'll fare better?