Wasn't able to find exactly what you wanted, but I've attached a couple of Images so it may help.
Keep in mind the "Fish Eye" effect is lessened considerably Underwater, mainly due to the Curvature of the Housing Dome, what you do still get is Fall Off to the edges & mostly the corners, using software for Underwater Images to "fix" the distortion is often a lesson in futility.
At 15mm the 8-15f/4 is just simply streets ahead of the older 15f/2.8, but it comes at a price difference, and the 8-15f/4 at less than say 14mm is of debatable real value (to me), although I have seen a lot of very nice Images even @ 8mm, so it's always going to be down to the user & their "artistic" view, someone posted earlier about the positive value of the older 15f/2.8, and they are right, it's a good Lens as well, it's just not up to the IQ of the 8-15f/4.
The Manta Shot: 5DMK II 8-15F/4, Shot @ f/7.1 & 1/125th ISO200
My Son's First Dive B&W: 5DMK II 15f/2.8, Shot @ f/8.0 & 1/125th ISO100