I installed the snapshot and was greeted to an insanely slow saved world. Breaking blocks results in a 0.3sec lag routinely though not guaranteed, start-up for the world is 5 times longer, chunks load longer as well. I checked the load on the C/GPU via task manager, the CPU was maxed 100% but the graphics was fine at most 50-60%. I reduced all the graphics and reduced the render and things became better (CPU at 70% is higher than normal though) but to go from fine maxed settings to practically bottom settings isn't the same Minecraft feeling. So I took the same save back to 19w35a and it was as fast as before (though the world reset) even as it created the 'New' chunks. The CPU load was only <53% and the GPU was 15% with the settings back at max. So obviously its the snapshot I think, but I want to raise this with someone so it doesn't continue to the official release.