I'll throw out a recommendation for the Camelbak MULE IF it fits your laptop. It'll fit m7 13 in Macbook just fine, no idea about a 15 in though. I got the newer version, with Camelbak's new airflow system, basically a few pads touch your back, then an inch or so of open air/mesh, and then the backpack starts. I have been more than happy with it so far.