U need to gain 15 KGS that too muscle not fat. I can help with 4-5 KGS weight gain in month that too muscle not fat.

Weight gain is a slow an steady process. Healthy muscle gain is what is required at your age. A balanced diet will promote muscle  and over all development. In case of non-vegetarians, there are lots of option to select from. For pure vegetarians there are many combinations of foods that promote muscle growth. I do not favour protein supplements unless you are a sports person.l Pulses, Soya, cruciferous vegetables, dairy products and whole cereals promote muscle gain. Along side proper exercise and a healthy lifestyle aids in overall developmemt. For tailor made diet plan feel free to contact me or register at http://ghkritediet.zest.md or drop in a mail at ghk.ritediet@gmail

Listen, you have to focus on your diet with much of protein and PUFA, MUFA type of fats. Increase your appetite by doing some pouch exercises so that you feel hungry but choose ideal foods to eat which help in muscle mass increase and not body fats. For that consult a dietitian.