Greater depth rating and the "push and hold" button controls are the big swing factors in favor of the Ikelite for me. Plus as an instructor and store staffer, I got a significant break on price for the Ikelite, which made it an easy decision. And I want to take it pretty deep and in frequent rugged/rough conditions. Looks don't mean much to me: function first, form second.
I haven't had the opportunity to see, touch, and use the P-015, but it sure gets rave reviews, and I believe that the camera manufacturer wouldn't make anything junky for their equipment. This is my first Olympus camera and first digital (several Nikon 35mms and a Canon 35mm), and I have been completely impressed with the C5050 so far. So if I was buying at retail and didn't plan on some of the constant abuse I am probably going to put the Ikelite through, I would probably have a PT-015.
Bottom line, if you can afford it and want to go deep with the easiest button control, go Ikelite. If you want to save some significant $$$ and get a high quality housing good for at least 100 feet, get the PT-015 and use the left over cash for more gear!!! Either way I think you can't go wrong.
Safe diving, and share your pics!