When I activate highly complex redstone circuits such as binary division calculator, severe lag, which is not found in other versions, is found.
The frame rate drops to 0 while the circuits are running.
This is noticeable when the circuits operate in a wide area.
In both 1.15.2 and 1.14.4, the lowest frame rate is 50.
This has been fixed in 20w28a, but it is still quite slower than 1.15.2 and 1.14.4.
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Please provide more details: benchmarks, screenshots, ...

Maybe duplicate of MC-190891

Please test is this is still an issue in the snapshot most likely releasing today, since MC-190891 has been fixed.

The rest is MC-192845.