Will walkin' for three hours a day 7 days a week help me lose 15pounds in 3 weeks?

Okay so last year when school started i was around 115-120. I now weigh 130-135. I've always had problems with the way i looked(weight). so weight is a biggg issue for me. So my question is if i walk for 3 hours in the moring everday will i at least loose 15 pounds in 3 weeks?