If you want to play normally you can just log in to 2b2t. If you wanted to play these snapshots in your own way then you'd need to decompress them and recompress them into normal Minecraft save format. You don't have to do the whole thing, (which is good considering the 15 TB figure is for the more optimally compressed version). At any point you can do this from disk. Only the chunks the Minecraft server/client have currently loaded in view distance need to go into RAM.