As has been reported last week the Nexus 6 comes stock with Encryption enabled. Many have reported some minor lag issues which seem to be tied to this feature. There is actually a way to disable the Forced Encryption. This does require a bit of adb knowledge. You will also need to be bootloader unlocked for this to work. Once bootloader is unlocked simply download the "Noforceencryption boot.img", flash it in bootloader mode (use fastboot flash boot command), then you will need to factory reset your device (use format userdata command, or you can factory reset in recovery), if for some reason this does not work you can flash the stock image in the bootloader mode. Run Cf-auto-root for root if desired. Head to the link below for the full guide. This should rid your device of all lag.
via XDA