It all depends on what you want. 17x15 is the equivalent of 9.3x8.3 in HO for example. If you want a continuous run then you don't have many options. JDunn has really maximized his space for continuous run. What if you don't want pop-ups or broad stretches that you can't reach across? Then an around the room is your option which pretty much dictates the track plan.
Your mileage may vary, but I have come to a point that it is more important for me to get the type of railroad that I want and not just take whatever I can get to get big trains running. If I have to drop to S scale or HO to get what I want then so be it. You may be fine with that though. Is it too small of a space? That all depends on what you want to do. If you really like yard or passenger operations you probably wouldn't have enough room. If you like the layouts posted above then you are probably in good shape.