There is a bottom line here ...
NO two phones are alike ! They have different sets of apps, running on Dev Preview, some coded better than others. Some apps are memory hogs, without proper garbage collection, thus memory becomes fragmented. A good practice (especially on some lower spec'd devices) would be to manage your open apps - if you have 10 apps open in the background, you are more prone to lag. ALSO, reboot your device, once a week, it'll do wonders for the phone.
Learned from my wife's experience, handed my Lumia 920 down to her, pick up the phone & she has anywhere from 5 - 18 instances still open in background. She also never powered her phone OFF. Now that she's powering off once a week, the niggling problems she encountered are gone - & she's still on WinPhone 8.0. She's also learned to close apps, rather than simply hitting the home button.
My Lumia 1520 is on Cyan (since Thursday) too early to tell, long term, but right now it's smooth as butter, very responsive, had 1 instance of 2 second lag since Thursday. Once your device gets the update, you'll see, a lot less lag ... because you're starting fresh w a re-install & because the firmware will be optimized to match the OS.
Patience & peace (both in short supply in the world, today)