I'm no expert, and not speaking from personal experience, but rather from what I have read. It would be hard to have too much FOC given that that arrows are properly spined. But it WILL definately affect arrow spine and tuning, and that is where it is important.
Are your new limbs lighter or heavier than the ones you currently are using those arrows with? Assuming that they are properly spined and tuned to your current set up, you might need to add or subtract weight from the front to tune them to the new limbs. If they are significantly different in weight, it might require a new arrow altogether.
I'm not sure what you mean by GT 15/35? I'm not familiar with that shaft designation.