They are not the same. The I515 is 0.52mm thicker - yet another reason it should not bear the name Galaxy Nexus. It may not seem like much, but my Otterbox Defender is a slightly sloppy fit, and the built-in screen protector doesn't make good contact with the screen near the edges, making registering touches near the edge a hit ot miss proposition. Adding a double-thick layer of business cards behind the phone in the case has helped greatly.
It's ridiculous that a manufacturer names two different phones identically. They don't share the same dimensions or even battery configuration.