As you mentioned ur child takes milk only , well that shoudnt be the case for 15mths old. Growing children need more nutrition. Also, its this time that the child refuses to eat due to two reasons teething
and taste.Give him mashed or grinded fruits and grains .This helps in 2 ways.
1. to swallow.the child finds difficult to chew due to teething.
2. the child may eat more because chewing whole grains makes the child tired fast and the child inturn eats less.
u can make upma in liquid form add little sauce ,can give dal ka paani. it taste gud and is healthy also.