Hi
My DS also didn't take a lot of milk but gained weight well.
After 1yo milk is considered a drink and the guidance is that bottles are dropped at this age. Some people do keep 1 or even 2 bottles a bit longer, but at 15 months it is totally fine that your Lo is dropping her bottles. It's time. She is older now and her main food source is solids, she will get the variety of nutrients and vitamins she needs from the solid meals rather than from the milk. It is also helpful for motor development and speech development for her to have solids rather than lots of milk. Your little girl is just growing up a bit that's all
I'm not 100% clear if she is still having a night feed - if she is I would totally phase that out now. It's better to drop any night feed rather before the day feeds. If she wakes at night comfort her with your usual method of verbal reassurance or a hand on her, cuddles, etc rather than feeding.
8oz of milk per day, sounds like roughly a cup which is totally fine for her age. This is giving her some fats and calcium. She might also be taking some yoghurt or cheese or white sauces with her meals, these count as dairy intake too. Even without cheese/yoghurt in her solids meals the milk is likely enough for a LO who has always taken less than 'average' so I do not think you need to be concerned
It is also possible to gain fats and calcium from other foods, some LOs cannot or do not take any milk at all so whilst there are guides on how much 'dairy' a toddler needs there are always exceptions and alternatives.
It is also fine to switch to cows milk if there is no allergy - I assume as she takes formula that she has no allergy to milk.
A common E routine for LOs this age is:
1 or 2 milk drinks (could be at WU or snack time or BT for instance)
3 solid meals (eating with the family, a range of grown up food and a healthy balanced diet)
2 snacks (LOs have small tummies, adults might not need snacks but usually children do)
Drinking from a sippy cup is a learned skill. You can sit her on your knee and gently encourage her by putting her hands on the handles and bringing it up to her mouth. One of the important parts of learning this is for you to only put a small amount of water in the cup, A couple of oz is plenty for learning. if you give her a full cup it is heavy and very difficult to control, let her learn when it is light, you can always add more water if she drinks it all.
You might also try her with a straw, dip one end into the water, put your finger on the other end to trap a small amount of water in the straw, then with your finger still on one end offer the other end to her mouth (demonstrate by you doing it first and telling her it is fine, nice), when in her mouth release your finger and the little bit of water will go in her mouth. Make sure she is sat upright so the water does not run to the back of her mouth. You can demonstrate the sippy cup and the straw by drinking your own drink in this way for a few days - I drank tea from a sippy cup for a few days to show my DS it was a good way to drink.
It may be that she had no interest in water because she was totally hydrated from the milk she has been taking. I would just keep offering water at meal and snack times and it may increase now that the milk intake has dropped.
If you feel very concerned about her taking water you could offer a bottle of water at the solids meal time but use of bottles should not be encouraged at this age as using a lot can effect tooth development (it's ok if it's a quick drink and only water or milk but it's a problem if a LO is drinking all day from a bottle). Sometimes LOs do need encouragement to move on from a bottle to a cup, show her, tell her, demonstrate and model the use of a cup.
I hope this helps.
