a close friend of mine ran 15psi daily on his MR2 with a japanese engine swap (ceramic CT26). ran it that way for 3 years with no problems. personally, if i were going to run more than 15psi, i'd be getting a larger turbo.
actually, i am planning on running over 15psi and i am planning on getting a larger turbo.
the difference between the ceramic and steel CT26s is somewhat noticable. if you're not planning on making huge amounts of power and want a very easy turbo to drive, then the ceramic CT26 isn't a bad choice. if you're planning on high boost or high revs, then look elsewhere.
-Mike