Only 15 pounds, but the worst 15 pounds

I feel really bad when I tell people I only need to lose 15 pounds. Allot of my friends need to lose at least 40 or more.
But this fifteen pounds is killing me. In the last three months I have stopped eating any kind of snacks whatsoever. No chips, popcorn, crackers, cheese, nothing. And I can not get this weight off.
I found this sight yesterday and downloaded the app to my phone.
I have always had a fast metabolism, back in the day. I fought to gain weight. At 5ft 1 it was a struggle all my life to stay over 90 lbs, so as you can imagine, fighting to lose weight is new to me, and I apparently am not very good at it.
My husband and I started power walking 3 1/2 miles 4 times a week and the only thing that has changed is that at least my weight has stopped going up.
I read about a 5:2 diet, what is that?
I don't want fads or quick drop diets as I feel that I will just be right back here again one day.
I used the app yesterday and input everything that crossed my lips, right down to the creamer in the coffee. I stayed under my goal for calorie intake and it says it will take me five weeks to lose three and half pounds at that rate. That's kind of slow isn't it?
Anyway, I am here and I am trying.