I have faced this in the past and obviously the best thing to do would be to find a new place to run. If that is not possible there are a range of masks out there that you can buy that are designed for fitness. I have tried one in the past but the airflow just wasn't good enough for me and I quickly abandoned it. Everyone is different in this regard though.
One thing I would be certain of if you do go this route is to make sure that you find a type of mask that elevates off of your mouth, IE not just one of those cheap drug store surgical masks because if you are like me, this will get clogged up with sweat and will actually make it difficult to breathe.
Running for 15 minutes when just started is pretty impressive. I wouldn't call that short at all!
Good luck!