New Tires

I just changed my tires for a lower profile 195/50/15 instead of 60s. Now the steering wheels is extremely light and the car feels unstable at high speeds. The car is pretty low already and then i put on the lower profile, could that be why? Or is it that i need an alignment. Another thing it might be that im riding on stock shocks. Somebody help. Why does it woble like that when i try to change lanes on the highway??