I recently flew from YVR (Vancouver) to DEL (New Delhi), and the time change there is 13.5 hours. What helped me is as soon as I got on the plane, I changed my watch to IST and slept and ate according to that time. I also found it helpful to land later at night as I could go to bed quickly and wake up somewhat in line with the local time. I was essentially fully adjusted on my second day there. Hopefully, this helps!