I've been running into this problem as well on a brand new 15" Macbook Pro with the NVIDIA graphics card. When I bring the same project into CC14 on a late 2012 21.5" iMac, it's no longer a problem.
Considering the SSD versus HDD, 16GB of RAM in the laptop versus 8GB in the desktop, improved graphics card, and i7 versus i5, I've been really frustrated by this problem. Not sure what would cause the disparity in performance as both are running the latest version of premiere.
Running native 5D footage in multicam sequences with anywhere from 2-5 cameras and it's a problem in every instance. Would love for word from Adobe on this problem and seeing that it gets fixed.