Nah, if you want the biggest mod ever then your looking for Advent of Ascension also known as Nevermine 2. Its a huge mod, takes up 40 megabytes, it also has over 20 dimensions and over 20 bosses. over 300 mobs and over 400 items. Way bigger than Orespawn.
Roughly 95% of Minecraft players hate Villagers and would be very happy if they were removed. If you are one of the 5% who actually like villagers, copy this into your signature and hope it never happens. ~EnderDude124
It's not exactly the largest, given some of the mods listed here, but the quality is far above any other mods I have ever found, so I might as well mention the Lord of the Rings Minecraft mod. it currently sits at a file size of about 24.7 Mb, but it is far from complete, and updates can often add another half Mb to the file size. I can't recommend enough that you try out the mod if you haven't. Here is a link to the official wiki: https://lotrminecraftmod.fandom.com/wiki/The_Lord_of_the_Rings_Minecraft_Mod_Wiki
Don't be discouraged by the fact that the mod is in 1.7.10, either. The mod is very much alive, and has a lot of its own mechanics, so Minecraft version is really mostly arbitrary.