Fifteen miles isn't all that far, so I would say get the bikes that you find most comfortable. You're really only locked in to the shop you buy the bike from for things which are included with the bike purchase (warranty issues, discounts on future service, etc.) For anything else, you can go to the closer shop.
At the beginning of the summer I purchased a new bike from a shop which is about a half-hour drive from my house. They had a really good deal on a bike I had my eye on, and I couldn't turn it down. But the bike turned out to have two separate problems. I had to take the bike back to the shop three or four times before everything got sorted out. It was all covered under warranty, and the guys at the shop were great about it. But I did get tired of making that drive. I only mention this to say that sometimes the distance to the bike shop does become an issue. But that's the exception, not the rule. Most new bikes are going to function just fine, and you'll only be taking them back to the shop for the complimentary tune-up after the new cables stretch.
And even if I knew then what I know now, I would still have purchased the same bike from the same shop. It's perfect for my type of riding, and it fits me well. So I would say the bike matters more than the shop.