Re: Anyone has tips for gaining weight here?
You are overwhelming yourself by thinking you need to gain 15 kgs because you don’t. That will put you on the higher end of healthy BMI. Your current BMI is just under 18 which is below healthy BMI so yes you do need to gain wt but only a few kgs. A total wt of 50kgs would put your BMI at 19.5 which is well within the healthy range. Increase your portion size if that’s difficult then have more meals/snacks but not the things midnight suggested 
Good luck.