Applying a large number of predicate overrides to an item in a resource pack will cause considerable FPS loss if the item is rendered too many times (example: armor stand head/hand slot).

Steps to recreate:

1- Download provided resource pack
2- Apply resource pack
3- Use the following command: "/give @p armor_stand 1 0 {EntityTag:{ArmorItems:[{},{},{},

]}}"
4- With the given item, place down 100* armor stands
5- Use the following command: "/replaceitem entity @e[type=ArmorStand] slot.armor.head diamond_axe 1 0"
6- Compare difference of FPS between diamond hoe (with 1,561 overrides applied) and diamond axe

*this number may vary depending on machine.

Code analysis by Schortan in this comment