Is it bad to break my 15 month old from the bottle at night if she eats full meals & snacks during the day?
No. It is appropriate for weaning an infant at about a year.
Put water in it. She may be eating at night out of habit. If you remove the calories from the nigh time feed, she will reset her feeding clock and quit waking for it. You can do this by decreasing the feed amount, diluting it, or just offering water. A gradual change allows for less fussing.