OlmecCraft

This modpack is intended for players who enjoy Minecraft’s core vanilla aspects: exploration and building. The pack features content from dozens of large content mods that enhance terrain generation, add new dimensions and progression, bosses, challenges, thousands of new blocks to the palette, over a hundred new mobs, supplement existing content and much more. The mods in this pack are highly configured by default to maintain the vanilla feel. 

I recommend you allocate anywhere between 6 to 10 GB of RAM.

The pack is also compatible with Optifine G7. (G8+ will cause immersive portals to crash on launch.)