I just bought a P2715Q (27", 163ppi) and I really haven't noticed the difference from my 220ppi 15" MacBook Pro. I'm sure if I put them side by side and shoved my face into them I would notice, but practically speaking, 163ppi is pretty great.
If you are using Mac OS, font smoothing makes it really hard to tell. If you are using Windows, the difference is more apparent given a more sharp font rendering.
This makes sense. I've also had a P2715Q for more than a year and it looks retina to me, but I'm mostly looking at the (anti-aliased) text when determining that.