Since version around ~1.7.5 Minecraft became sluggish and freezes randomly all the time.

edit: it actually isn't that bad on 1.7.10 - so now only snapshots are problematic

It's probably due to too many temporary objects being destroyed and garbage collected... Even if garbage collector manages to do it's job on time, it's not good as CPU usage is 100% all the time. (and it's noot good)

This video demonstrates the issue on skyblock map http://youtu.be/YHJBRd5pBxg heap usage jumps like crazy
And this is how it works on older version http://youtu.be/VVNN4BUpKHs

Using skyblock map was just a personal preference here. The same thing happens with "normal" minecraft maps.

No mods are installed. (and actually, optifine solves the issue for 1.7.10 version)