Try sizing up the nipple! We have dr browns and on nipple 2 since 3rd week. She finishes 3 oz in 8 minutes. We’re 5 weeks today so not quite there yet for 4 ounces
Mine used to fall asleep with nipple 1 to only wake up to feed again and it was like that for like an hour as well. Then we tried one bottle with nipple 2 in a more upright position so in case it overflows in her mouth and she chokes, it’s easier to pat on the back, and it worked very well!
Mine takes an hour to drink about 4 oz. We changed the teat to 2 but she still takes a long time as falls asleep and is also spitting a lot out
My 5 week old drinks 5 oz in about 20 mins (size 1 teat)
5oz takes 15 mins. Maybe check the latch or make sure teat is best for LO? Not sure it should take that long but I could be wrong x