Well I wouldn't say drop the milk altogether, but by 14 months DD had no more bottles of milk, we dicreased her milk to 16oz because she eats a lot of milk foods, I think by 22 months you can drop the 2 bottles, increase milk food intake and keep sippies or cups of milk during the daytime, meals are a great time to have it.
When your LO wakes give him Brakefast and just have a cup of milk with it, and at dinner have his cup of milk with dinner, he shouldn't need a bedtime bottle.
Yaya cut back on the bottle, try sippies instead, as he gets used to them he'll take more, but don't be alarmed if the first few days he drinks little to no milk, just make sure he has cheese, yogerts, and other milk products. By 15 months the main nutrition should be from solids. As your DS drinks less he'll balence that out by eating more. It'll take a few days for ajustment but it'll happen, when he starts to eat more solid foods he'll wake less to eat too and eventually not wake at all. This is what I did with my friends 14 month old when he was staying her overnight. I cut his milk in half and cut juice right out, he was having 45-50oz a day of liquids and needing to feed at night to make up for it.
HTH