It is sooo hard to stop especially the older they get. I have 3 children. Two older boys - my first I stopped breastfeeding at 4 months but he started on a bottle at 2 months. My second breastfed exclusively for 12 months and weened easily. My third, my daughter who is now only 3, was IMPOSSIBLE to stop. I tried and tried and tried and sounded just like you. So hear comes some MORE advice for whatever it is worth to you. Maybe something in it will help.
At 15 months, my daughter would not take any other kind of "supplement". No milk, no formula, no Pediasure, nothing. She did eventually wean after 2 years which was too long for me- I know that sounds bad but society, friends, family make you feel bad about it. I was very worried and she did breastfeed a LOT longer than I ever planned, wanted to, needed to.
Obviously, your daughter still needs it and according to most breastfeeding experts what you are doing is NORMAL and part of it. However, in the US and our society makes us feel like we are doing something wrong. And in some ways, I felt better knowing I was adapting to what I needed to do to feel my best. So, whenever I was cutting out a feeding or trying to cut out the habit of her falling back to sleep nursing, I started to just cuddle with her more and lay down to go to sleep with her reassuring her Mommy is there and if and when she woke up I would soothe her back to sleep by holding her even staying in the bed. I also tried to let her take more right before bed. She did not end up stopping all nursings until age 2 though and more like 26-27 months so I wasn't as worried about other sources of milk fat by then and she loved ice cream. My second child weaned onto rice milk (sold in carton). He loved it when it soaked into rice krispies so they were soggy (almost like the mixed gerber baby cereal ) but with more texture. My daughter would not drink that but she would put it on cereal when she was a little older than yours. To this day she will not drink much milk. We tried chocolate milk which she will drink some. She LOVES yogurt and ice cream and that worked for us. I too was concerned at 15 months and wouldn't advise cutting cold turkey at this point. She is still young and even my bottle fed baby still had a bottle at 15 months. They have an innate desire to suck until 2 yrs. She would NOT take a pacifier. Both her and my 2nd son did not sleep through the night until they were 2 years old, he was weaned almost a year and still didn't sleep through the night! One was still breastfeeding the other was not. My first started sleeping through the night at like 6 months but I could respect his schedule. My daughter goes to sleep on her own NOW and is fine and hasn't nursed in a year. She has slept through the night from about 18 months on even while still breastfeeding. I wouldn't try cutting out nursing and having her go to sleep by herself at the same time. Take each new thing one step at a time. That worked for us and again mine was older than yours but I started trying to stop breastfeeding from about 9 -12 months! Actually, we never stopped trying to give her a bottle since she was born even with breastmilk in it. She refused any bottle, pacifier anything. We tried every sippy cup, straw, bottle, nipple, etc.... she refused. I know people say if she gets hungry enough she will take something else but mine wouldn't and even if she had her food, if she missed a feeding it seemed like she was clingier and more attached and determined to nurse after that. I won't let them cry it out for HOURS as some can. There is some crying and discomfort and a little is necessary but to ignore them for hours, with a baby just crying to me is inhumane. That method did not work for me for any of my 3 kids and me.
So I started to relax some and act like its no big deal and do what was needed. Slowly changing our routine and how we did things and that worked the best for us. It is SO hard I know and I feel for you. Do what works for the two of you given where you are at, for rest and health. I quit telling anyone I was still breastfeeding and avoiding the subject when she was about 18 months old due to negative reactions, unsolicited or judging advice and did what worked for us. Watch for her cues especially the older she gets and try and cut one feeding out at a time every month or so. Be there for her. It seemed like the more I wanted to stop and the more frustrated I got it seemed like that is when she really wanted to nurse and even moreso! I wouldn't try cutting out nursing and having her go to sleep by herself at the same time. Gradually and one step at a time worked for my daughter. I feel for you and your question brought back a really tough time in my life due to it all. It wasn't fun but she is healthy and hopefully the breasfeeding that has been done will have unforeseen benefits. Take care and good luck!