Upto six months breastfeeding only recommended for babies...
After that only you can start giving semi-solid foods along with bm or fm...

So now you can continue only breast milk...

By 5-6 months babies weight could be twice of the birth weight...

Can you explain your question more clearly??

Yes

Weight gaining foods are..... Banana,, potatoes,,, eggs,, dryfruits,,, paneer,, ghee,,, cheese,,,pulses,,, full cream milk,, all dairy products ...u can give pediasure in milk,,, or u can make milkshakes by adding fruits or dryfruits,,for breakfast......,..suji chila,, besan chila,, upma,, oats,,, and homemade food which u prepares for the family.... No need for any specific diet at this age... U can give same food which u prepares for other members...if ur baby likes sweets... Make laddoo,, halwa,,, kheer... with less suger and add ghee..... Aalu paratha,,, veg stuffed paratha,, etc.. if baby isn't eating same food then try to make his fav. Dishes sometimes.... And to find out any deficiency or any certain reason...consult dr. Once...

I have worksheets for 3momths subscription. If you wish you can try. Bit its too early to ask them to write. Let the baby enjoy, read stories , sing rhymes

At this age weight should be around 9 to 10 kgs... Or could be 11.....and 15kg is too much for a year old baby.... This is the weight of 2.5 yr old baby.... Is ur baby active.. if he is active then it's fine but once check with dr. Bcoz it can lead to many health issues in future... So once consult dr. It will be better....they will advice u...

Ideally weight should be b/w 15-18.. kgs.....

Okay... Then once consult dr. May be it's due to any kind of deficiency... Or stomach worms... And if u r not giving iron n calcium supplements.... they will prescribe ..... If needed....for weight gain.....give homemade food,, cow milk,,, egg yolk... Or dryfruits powder in milk....mashed banana,, mashed potatoes,,, avoid packaged food... Bcoz packaged food reduces appetite.....

What was the birth weight n present weight...

If he is saying few words then nothing to worry... Keep talking with him... Appreciate when he speaks.. Give him fun task where he has to say a sentence so he will get something in return ...
My son also was not interested in speaking, so when he asked for water i made him say complete sentence then only i gave water... This way he picked up quickly.. Try this and be gentle and patient.. If you will shout he will stop talking out of fear...