No chance it'll last 15 years. The industry wouldn't be able to cope...
10 years is much more likely for PS3. With PS4 coming out in the 7th or 8th year ...
Though i believe that the next-gen consoles will not offer us huge graphical improvements. Instead the additional power will provide us with other features such as larger zones / less loading, more enemies on the screen and possibly dual-control systems -> eg. Wii-Mote + Sixaxis







