Whilst the Classic Kånken from Fjällräven will just about fit a 15" Laptop inside, if carrying a laptop is essential to you we'd recommend the 15" Laptop Kånken as a better choice. With an additional, dedicated laptop compartment in the back (which is both padded and lined for protection), this model also has the thicker straps to help distribute the weight of your laptop for more comfortable carrying.
Illustration of a Cabin
The Brokedown Palace