Kids should be able to walk without support when they complete 15 months.
When they learn to walk, if they fall and hurt themselves, they can temporarily stop walking.
You can encourage him to walk with support of wall/ furniture etc or by holding his hands. He will be okay I guess.
His speech seems to be okay. Just keep speaking to him, teach him identify objects from picture books, sing rhymes to him and tell him stories.
His weight seems to be on the lower side. Just see his centiles in his growth chart
. If he maintains the same centile, its fine. If there is a dip in the centile curve, you must speak to your Pediatrician
Fortify his food items with ghee/ oil/ cheese/ butter etc. Reduce his milk intake to 3 cups a day. Give him more of solid food. Give plenty of nuts and dry fruits.
Hope my answer helps you.
Wish your son good health.