I noticed the same thing but even if I disable “Fourteen colours”, it’s still really slow. By that I mean in the customization it just creeps along. “Styles TwentyFourteen” seems like a nice plugin but I just can’t get it to work, so I only use the two in combination that you mention. I’ve even tried disabling all the other plugins associated with my theme “Twenty Fourteen” (except “Styles”) and there’s not much of an improvement.
