nipple size

my son is three months old and for the past few days he’s been falling asleep while eating. this doesn’t happen everytime i give him a bottle, but like 8/10 times lol. he’s strictly bottle fed formula. he’s on size 0 and 1, he used to choke on his formula with size 2 nipples. does him falling asleep mean i should move the nipple size up to 2?