If anyone is having LAg or issues, I personally also believe it's not due to the chip information we do know, it's due to IOS9 and its problems.
Have a new mini 4 and there are issues in apps and IOS9 B340 that are not present on IOS 8.4.1 on my mini 2 and IOS 8.2 on my Air 1. They have less ram and older cpu/gpu yet most apps I use were developed and optimized for IOS 8 and work smoothly with no bugs, glitches, hitching or lag which includes games and productivity apps.
Same apps on newer hardware which is faster with more ram, these games and productivity apps are lagging off and on, hitching (stuttering frame rates during animations and transitions) and we got the delay from touch clicking them to load and then loading slower itself. Also the CC, task switcher, pull down thing i.e. And spotlight search always lags off and on if its already in ram loaded or not.
None of these issues in IOS 8, every time I do a full charge from shutoff dead mode on my mini 4, after I get it to 100 percent and let it charge a little more, I do a shut off and restart, and then you can really see the IOS 9 issues after it reboots into the homescreen while it starts everything in a fresh state.
Once again IOS 8 does not do this. I know it's frustrating and troublesome but all we can do is wait for Apple to sprinkle some ferry dust on the software, release updates and let the OS and apps mature. Hopefully one day it will be smooth sailing again in calm waters on a nice spring day.