eat less food

I started eating a lot when I was very stressed due to loosing my job about 2 years ago, and it became a habit. My stomach got used to the larger quantity of food, so I wouldn’t satisfy my hunger if I ate smaller portions. Thank god I have a pretty fast metabolism, otherwise I would be not just a little fat, but really fat.
I have started eating less for the last couple of days. Today I left half of my Reuben untouched during lunch. (-: I’m hungry now though.
My weight is 120 lbs. and it needs to be 105 lbs. I have 15 lbs of fat on me that I have acquired in the last 2 years.