Folks at XDA have released Moto E 2015 book unlocker and relocker tool that easily allows you to unlock Moto E 2015 by pressing few buttons. The very same tool allows you to install custom recovery into the Moto E 2015, allowing you to install various custom firmwares and hacks.
To install, you must have NET 4.0 installed in your system. If you do not have it, you can install it from here.
How to use boot unlocker Moto 2015 tool
Turn ON USB Debugging Mode under Setting>>Developer options
Select Allow OEM Unlock
Open Moto E Toolkit
Click Download Drivers button and then install it.
Click on Check Devices button, your device will be listed
Unlocking Bootloader
Warning: Unlocking Bootloader Will wipe User data take Backup of your contacts, msgs, apps etc
Click on Generate String Button,
Device will reboot into Fastboot mode and website will be open.
Login into site,
Copy String from application and paste it into website text field and clicking “Can my device be unlocked?”
If your device is unlockable, a "REQUEST UNLOCK KEY" button will appear at the bottom of this page
Select I agree, and click on REQUEST UNLOCK KEY,
Copy Unlock Key you got in your mail and paste it into Application text field "Enter Unlock Code" and click on Unlock
Done