A question: Did you shoot this film in daylight or flash? If so, there is a huge part of your problem. It is a tungsten-balanced film.
FYI, "blue" in color printing actually looks more like what most would call lavender/purple. This explains why using yellow to alter the cast was working better.
My first suggestion would be to go ahead and zero out the yellow. You are already at only 15, so why not go all the way? What stopped you?
Then, when you are out of yellow, start using your cyan filtration. Upping that filter will add red to the print (which is equal amounts of magenta and yellow). You can use magenta filtration to counteract the magenta that is introduced when upping the cyan filtration, while leaving the yellow there. To start I would do it like so: Whatever you add in cyan filtration, also add half as much in magenta filtration.