baby drinks milk too fast from preemie slow flow nipple, never satisfied

I've had to pump lately due to thrush which has been major headache and agony. I feel so bad because our baby likes to take his time eating like 30-40 min per breast, always feeds both breasts. The bottle takes like a few min not even and he is never satisfied and drinks too fast. He is coughing and spitting up on about 4 oz and seems he wants more.. using a preemie slow flow nipple too. Suppose to be the slowest. Still only takes a few min.