After update to CC2015 I encountered very annoying thing, It is probably caused by this "video system overhaul" that gives you ability to change sliders while sequence plays.
To the point:
Create camera tracker on any footage that can be tracked. Start to scrub timeline. You will notice that cross markers are laggy in relation to underlying video, this gives you an impression that they don't match. Only when you play manually frame by frame, the trackers sit where they really are. The same is with mask tracker. Take any footage, create a mask and start mask tracking - similar situation occurs - you don't really see if it sits correctly or not until you check manually by pgup pg down keys.
Now open CC2014 and do the same procedure abobe. Camera Tracker points and masks sit solid without any lagging, whenever you scrub.
There is clearly something messed up with new video playback overhaul.
Please inform me if you are aware of this issue and do you plan to fix it. Right now I am mainly working in CC2014 because of this.
try opening your preferences to the display tab and check or uncheck hardware accelerate for your display.