P2715Q response time very slow

I would hold off on returning it until you are sure you are running it at the full 60hz, it may well be running at 30hz for you at the moment, that would indeed make it feel extremely laggy with the mouse.  The response time modes (game/fast) are just slight tweaks to the millisecond refresh and are probably not the issue.  You want to see if it's refreshing fully at 60hz, which is a different thing.

Mine should be arriving today, but I think I remember it displaying the resolution and hz refresh on the on screen display menu when you change inputs, brightness etc.

So, verify it's running at 60hz first, if it isn't it might be an issue with the connection.

Thanks for the help ScottB.  I checked the on screen display menu and you are right - it's running at 30Hz.  I cannot find a way to switch that to 60Hz.  Neither the monitor menu nor the Mac OS display preference allow for that.  Going to look into third party apps that allow you to adjust the refresh rate.  

Any thought on what the connection issue might be?  Maybe my mDP to mDP cable is the culprit?  Unfortunately I can't get the supplied DP to mDP cable to work on my setup in spite of switching inputs, power cycling, etc.  Also tried a Thunderbolt cable with no luck.

Ok, I'm pretty sure that the display is not faulty, so no need to return it.  It's not a case of switching it at the monitor side, it's to do with sending the right signal/connection from the computer and/or right cable then the monitor just detects what's it's getting and displays it.

Also verify that you are using DisplayPort 1.2 and above to support that refresh rate.

It seems that other users with Mac's using the Thunderbolt to DisplayPort are having issues getting it to 60hz (mac/connection issue, not monitor):

discussions.apple.com/.../6605359

Here's another thread:

forums.overclockers.co.uk/showthread.php

ScottB,

Thanks so much for your very helpful posts - I really appreciate that!!  I've made some progress with the refresh rate issue after downloading SwitchResX and fussing around with the various options.  I think my Mac OS (Mavericks - 10.9.5) is the main issue.  I hear Yosemite (10.10) is an improvement for folks with 4K displays.

Right now I've got the Dell and the Vizio running at 1080p / 60Hz (120Hz on the Vizio) and the lag is much better.  At 2560x1440 (both at 60Hz) it seems like lag increases but it's pretty subtle.  I may be going a little crazy but compared to 30Hz on the Dell, text resolution doesn't seem to be quite as crisp but it's still better than previous monitors I've used and the screen real estate is nice.

Again - thanks for the info.  Just read through the links you posted and am finally realizing that 4K isn't quite plug-n-play yet!  ;)

Glad to hear you're making progress.  Yeah I was a little unsure about going 4k just yet as it's early days and there are still issues to iron out.  But I know these things will get fixed over time and this screen is set up to be future proof.  My only worries are some software packages that I use having extremely small text and icons that can't (yet) be adjusted for high DPI monitors.

Happy new year btw and best of luck with the monitor!

:)

Yeah - discovering the icon / graphics incompatibilities here as well...

Thanks again and Happy New Year to you too!