I am running 15 in the rear in 14.
And the front... I also bought new brake hoses Front end rear and a new proportioning valve.... Justin case Is justin case. The new hoses and proportioning valve have not been installed.
Sure but what tire sizes? The rim isn't really a big deal, it's the overall tire diameters and widths that really change the braking balance.
The prop valve controls the whole brake balance, but as long as it's working properly replacing it isn't going to change much. Now if it's stuck I suppose that could mess with your front/rear bias, but usually that results in more extreme issues than what you're having. Plus it wouldn't effect a single brake, it would be both rears being altered.
The hoses obviously could affect one side (depending on which hose we're talking about).