FFOF is fairly hot out of the bag and if you've been adding nutes on top of that, it might be a little rich in there. But hey, as long as things aren't spotting or curling and they're happy-looking, you're good.
If you're going 12/12 soon, the nitrogen supply will get used up quickly when they stretch. Stick with your 15-10-8 until the height growth levels off.
Good luck...