It could be balance but 25 is pretty slow for a balance problem to show up. Usually bad balance starts to show around 45 to 55. But since they are new I would take it back and have them balanced again anyway. Rotating the tires might mask the problem so make sure they put the tires back in the same positions. If the vibration persists then try rotating front to back.
Can you describe the vibration you are feeling? Does it feel like a buzzing type of vibration or does the wheel wiggle side to side? If a buzzing it might be a harmonic from the design of the tire tread.