Performance drop on mobile when viewing inside of complex model

Verification builds: Release 1012412
Summary: A significant FPS drop occurs when viewing the inside of a particularly complex model (resource pack attached). This was observed on two mobile devices but not on Windows 10.

Impact: Performance issues when colliding with a mob.

Repro Steps:
1. Download the attached resource pack onto a mobile device.
2. Open it, such that it imports into Minecraft.
3. Enable it in Global Resources.
4. Create a new flat creative world.
5. Spawn several zombie pigmen around the world (the model should appear as in the attached screenshot).
6. Observe the game performance (it should be fine).
7. Walk inside a zombie pigman to view its model from the inside (an easy way: mine down two blocks and spawn the pigman in a hole, then jump in with it).
8. Observe the game performance (it should be significantly more stuttery until you stop viewing the inside of the model).

Expected Results: Performance impact is the same, inside and outside.

Screenshots/Videos attached: Screenshot of model in-game and attached resource pack.

Notes:
I know this is kind of a vague, abstract report, but it is definitely noticeable and strange behavior. TRS observed the behavior on a LG90 and myself on a OnePlus 5. I could not reproduce on Windows 10. Please feel free to solicit more information from me.