I'm making a pvp map and are using the snapshots to help me. I made a commandblock with the /testfor (and some other stuff) in it so i could detect when someone is on a certain block and when I updated to (I think) 14w8a so was the clock going slower. SEE VIDEO BELOW. (it may just be the command)
Link to bug: https://www.youtube.com/watch?v=ercr2s1GPNo&feature=c4-overview&list=UUUAmSMu5Do5uODRd1GgWbRQ.
The clock with the commandblock attached to it seems to also slow down the other two clocks.
You could attach some of your system specs (maybe because of the snapshots testfor commands became way more memory intense and your computer doesn't have quiet enough ram). And you could also look whether the chunk the commandblock is testing for is already loaded when near these two clocks (otherwise the commandblock could continueosly load and unload the chunk which is possibly causing these slow ticks).