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.
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.