Tremendous-1500 is one of the biggest "normal" Universes known to exist. It's contained within the biggest megaverse and the biggest multiverse.
Its name is quite easy to understand. "Tremendous" because of its size, and "1500" because of it being around 1.5 quintillion light years large.
The main civilization that lives in this verse is known as the Tremendousians. The civilization has tried to expand the universe, but to no avail. The biggest thing IN this universe is the Leo-Taurus Hypercluster Supercomplex.
Tremendous-1500 is often mistaken for a Multiverse because of its size.