Walking does burn fewer calories than jogging or running.
But please don't give up. Just increase your walk 10 minutes every week. You'll notice that you can go on longer as your body gets stronger. I read somewhere that if you want to maintain your weight walk 30 minutes 3-4 times a week. For weight loss it's 45 minutes. I just throw in the extra 15 (totaling 1 hour) as a bonus (extra credit). Then you can try to add a little speed (speed walking) and that will help burn more calories in the same amount of time as regular walking. Before you know it, you'll be losing weight in no time.
I currently speed walk 8 miles in 1 hour and 15 minutes. At 140 LBS I'm burning over 700 calories.
Slowly train your body into fitness mode.