What I would do is, not turn eating into a battle. It will make meal time something to not look forward to.
Its fine to give him Formula/Toddler formula still. My Pediatrician recommended that for my picky son. Although he did drink milk.
What I also did is: on a tray, I put finger foods cut up into proper sizes (to prevent choking) and I'd leave it on our coffee table... so that my son could "graze" and self-feed.. .and when he was hungry. I also put out a sippy cup or straw cup of milk... or water. I do NOT give juice until after 2 years old if anything. Too much sugar.
You don't have to stop bottles... because if he will NOT drink anything unless from a bottle, then you need to offer him Formula/milk in a bottle so that he will drink and get in his nutrition. Stopping bottles can occur later... once he does get the hang of sippy cups/straw cups.
But put them out and make it available anyway. Just to expose him to it.
My kids, HATE high-chairs. You do NOT have to only feed a child in a high chair. Make eating in a way that is applicable to them.
My kids, by my leaving out a tray for them on the coffee table... was more prone to eating this way... because it was not forced... and they went by their cues for hunger.
Eating, is not a rigid thing. Being rigid about it will only make the kid HATE mealtime. Do what works.... he is only 15 months old. Don't worry about it.... there is lots of time for them to mature and learn manners and routines about eating. Not at this age.
And yes, at this age, they throw food. But when he does... take him down, stop feeding. No need to make it a battle. Or it will become a routine for him.... you don't want him to learn that about eating.
Just cut up in small pieces things he does eat. Put it in little bowls on a tray... along with the sippy cup or straw cup of water or milk. Its more friendly that way.
And yes, kids this age DO tend to over-stuff their mouths... thus, you need to supervise their eating so they don't choke. Don't expect him, at this young age, to know about portioning in their mouth. My son is 3.5, and he still over-stuffs his mouth sometimes. So you need to supervise.
Babies this age, do NOT have impulse control... and full impulse control is not even mastered in a 3 year old. So, keep expectations age-appropriate. Otherwise it will be frustrating.
All the best,
Susan