Significant performance regression in 25w16a

To start off this report is not a duplicate of MC-295893 as this report concerns a performance issue in 25w16a, not 1.21.5.

Anyways as the title states, the overall performance got significantly worse in the latest snapshots.

Here’s the performance in the past few verions from my testing:
- 1.21.4 600 FPS
- 1.21.5 530 FPS (-12% vs 1.21.4)
- 25w15a 570 FPS (-5% vs 1.21.4, +7.5% vs 1.21.5)
- 25w16a/25w17a 400 FPS (-35% vs 1.21.4 -25% vs 1.21.5)

What’s interesting is that performance improved in 25w15a and nearly brought the performance back to 1.21.4 levels for me.

Reproduction Steps:
- Create a world in 1.21.5 with all mob spawning disabled
- Do /kill @e[type=!player] a few times to get rid of all entities
- Wait 2 minutes for the frametimes to stabilise
- Check the FPS
- Load into the same world in 25w17a
- Disable clouds for good measure (isolate out whatever impact their recent changes might have had)
- Wait 2 minutes for frametimes to stabilise
- Check the FPS

Note: When “checking the FPS” keep the GUI hidden and only look at the FPS value on the first frame after unhiding the GUI (to minimize impact from GUI rendering MC-296911)

Observed Results:
- There is a significant FPS loss in latest snapshot when compared against 1.21.5

Expected Results:
- There wouldn’t be FPS loss