In the recent snapshot, the game seems to dramatically decrease it's tick speed when it's faced with a lot of command blocks. My map does have a lot of command blocks, and it used to run just fine, but now the tick speed is slowed by about 5 times, therefore making the map unplayable.

How to replicate:
I am not completely sure what causes this, but I am almost sure that this is a bug with the new data structure and the new rendering of blocks. Try this: Make an ordinary 5 Hz clock, and then make a 20 Hz Clock and hook up as much as you can to it, and you should see the 5 Hz Clock dramatically slow down.