Well I'm a "hands on" kinda guy, so I would opt for the ported setup and make some minor tweaks, if needed. The 15" space you described should be fine for any practical setup.
However, if you plan on concert levels, the ports may cause some minor issues. As long as the ports can breath around the other equipment, you'll be fine.
When building ported speakers, the rule of thumb, is to keep the port away from interior walls by at least the diameter/size of the port. For instance a 3" diameter port needs to be at least 3" from any interior wall.
While this isn't true of all setups (sub woofer systems can and do use different methods), bookshelf speakers should be practically unaffected as long as some space is dedicated to allow for the movement of air from any of the loudspeaker's output surfaces/area's. Come to think of it, a set using passive radiators may work even better for you.
That being said you can expect some over enforced bass lines, possible standing waves, and phase issues depending on your specific setup. But these should be minor unless you're really cramming everything together in one spot.
Although not applicable to your setup, the best sounding sub woofer setup I've ever heard is the Double Eagle system from Shahinian Acoustics. It uses four 8" drivers and four 10" passive radiators (two of each per L/R channels). Have you ever heard 5Hz at volume? Frightening enough, and even more so when you realize those are just a couple of 8's playing!
You probably already know this but the passive radiator design (when done correctly) eliminates the port noise that can be generated sometimes at volume. And do so without a loss of performance. In my case I've even achieved "better than ported" results when utilizing passive radiators. Their use is still somewhat of an art and requires a lot of forethought (experimenting) on the driver performance, cabinet design, and getting the radiators to match up with everything.
Sorry for the long answer, but I hoped I helped.
Andrew
Synesthesia Studios