Can I ride on 15 spokes instead of 16?
You shouldn't ride on a wheel with broken spokes more than necessary, especially if its a low spoke count wheel (like a 16 spoke wheel). The load gets unbalanced with respect to the other spokes. 

Since this is a front wheel, I wouldn't risk riding it. If something does happen to the wheel (such as failure) its far more serious than if it happened to the rear wheel (you can recover from rear wheel failure; recovering from front wheel failure may require you finding your teeth on the side of the road).