So my daughter has taken to the NUK perfect fit nipple pretty well, but i’m noticing it’s taking her…

So my daughter has taken to the NUK perfect fit nipple pretty well, but i’m noticing it’s taking her forever to drink. I don’t really know how because it’s a medium flow. But she was drinking for like 5-10 minutes and only got an ounce out. Should I get her the next size up? Does anyone else have this problem?