How to make my LO drink all at once?

Hi all. My LO is currently 2 weeks old. By right she should be taking around 90ml formula milk. However, these few days, she has been drinking only 30ml each time and within the next 30mins-1hr she will ask for more milk again. We can take 1.5hrs to finally finish feeding her 90ml. Any idea how to make her drink all at once? Is it because the bottle teat size is too small?