Help and advice needed for 15 month old that doesn't chew properly

If you're really concerned and feel like you need a second opinion, you can consider looking into and/or asking your pediatrician about feeding therapy: https://napacenter.org/how-does-feeding-therapy-work/

My youngest had difficulty leveraging his tongue properly to move food around when eating, which would then lead to choking on even purees and really small pieces of food. This was something that feeding therapy was able to help with. Depending on what the actual problem is with your child, feeding therapy may or may not be useful.

I've been amazed at how much my 3 kids have learned by mirroring. Are you eating with your baby? It might help him to understand what he needs to do by seeing you eating face to face with him. Even possibly you could consider really exaggerating the chewing motion so he sees what to do.

I wouldn't be surprised if he even started copying you without being at a meal time if you just made eye contact then mimed chewing.

I was nervous about choking too. While many of my friends and colleagues went the BLW route, I started with purees. I think at 16 months I was not yet comfortable giving my baby a piece of apple that wasn't thinly sliced.

As another answer said, choking and gagging is totally normal, this is how they will learn right sized bites. One thing that helped ease my anxiety was to get really comfortable with the baby Heimlich Maneuver. That helped me feel confident that I'd be able to move fast if she were really choking.

No matter how he looks, or what sounds he's making, if air is going in and out, he's breathing, which means he's fine. It's not comfortable to hear your kid cough, but if they are coughing, it means air is going in and out, so they aren't in danger.

This is a normal, age appropriate behavior. He'll get better with time and practice. As scary as it is, gagging from over filling his mouth is how he learns about appropriate bite size and chewing. It was frequent experience when my child was that age, and still sometimes happens, although far less often as he got older, and is rare now at 3.

For my son, I didn't try to discourage spitting out food as a toddler (this aspect of manners can come later). I told him, "If it's too big, spit it out and try again with a smaller bite". The ability to push something out of the mouth when it's not able to be comfortably swallowed is also a valuable safe-eating skill, and it's normal for babies to practice it even if not appetizing to witness during meals. As he got better at eating, I didn't have to say this as much, first because he would spit out too-big food on his own before gagging, and then because he knew not to take huge bites and how to chew.