Is it unusual for a 15 months old to fill her mouth with food? She does this fairly often, especially with food she likes, then she realizes her mouth is too full and spits.
We tell her to chew and to take a piece at a time, or to bite off chunks, but it doesn't work every time.
I don't know if this is relevant, but she has always been a fast eater, she was breastfed and it took her about 10 minutes for a full meal