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.
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.