How long should feedings take?

I’m basically exclusively pumping at this point and using Dr. Browns bottles since my baby was born. She’s always done well with them but we recently tried to graduate from the premie nipple to the size 1. We had originally used the premie size because someone told me it was the slowest flow and most similar to the breast. However, she was taking nearly 30 minutes to feed and falling asleep. Well now with the size 1s, it takes about 10-12 minutes. BUT I’ve noticed a definite increase in spitting-up episodes so I’m torn about which size to use. Also, she takes about 3.5 oz at a time and will be 4 weeks on Friday.

Any thoughts or anyone have experience with these particular bottles? TIA!