A: By the age of 15 months, you should be able to move past using the bottle or holding him to soothe at bedtime. Unfortunately, if this has been his routine for 15 months, he may not undersetand how to self-soothe and go to sleep without your involvement. Changing this habit will take time and persistence, and there are several schools of thought on what the best method might be.
Regardless of the route you take in the end, the first step is starting a consistent bedtime routine around the same time every night (bathing, brushing teeth, reading a story, and then tucking into bed with or without soothing music in the background). Once the bedtime routine is established, you can stop giving him the bottle and holding him. Allow him to "cry it out," but know that there will be days (and up to a week or more) of screaming and possible vomiting while he works it out on his own. If you can handle fussy days and nights (where no one in the house will get much sleep), this routine will likely have the desired result in the shortest amount of time.
The other option would be to place your child in bed and then sit in a chair next to the bed. Reassure him verbally that he is ok and that he can go to sleep while you are present in the room. If he tries to get out of the bed, say that he is a big boy and that he can go to sleep. Repeatedly lay him back in the bed. This may take a few hours the first few nights. Once he is more comfortable with this routine, move your chair back a foot or two every night until you are outside the door. This method may take up to several weeks or months before he sleeps along without a bottle. The most improtant thing is to be consistent in how you approach either options because even one night of giving in (holding him or returning the bottle) will make him put up a fight and it will take much longer the next time you try to break his bad bedtime habit.