Agreed – used both extensively now, the U2515h is a better monitor, in particular the anti-glare coating is far less obtrusive (though I do like the new stand).
And a different screen ratio. Ones 16:10 and ones 16:9.
Might not be a deal breaker for you but the u2415 has a 24" screen and the u2518d has a 25" screen.
Get the U2415h. A lot better I reckon.
This replaced the U2515h. I've been using this one for a few months. I was using 2 of the older models. A good price, but not as good as the previous model.