DD is 15mths and still having 2 bottles a day - one on waking and one before bed. She never falls asleep with it in her mouth and will occasionally have a 3rd bottle during the day if she is teething or sick..
She is also on soy formula and milk as she has a dairy allergy and my doctor advised her having bottles of formula until she is at least 2. That way she doesn't get used to a cup with formula in it and will make it easier for her to drop later when she is ready. I'm not fussed at this point - we let her lead the way and it works for us.

I wouldn't stress. If it's working - leave it be..