If you want to keep full stock, yes. The steps are as followed:

• Downgrade to 10b or 11c (I recommend 10b)
• Root with Stump (10B only) or IORoot (10B and 11C) (Stump is WAY easier)
• Install SuperSU (I don't know if you need to with IORoot, but I have only used Stump root)
• Enable Survival Mode
• Upgrade to 12B via OTA
• Profit

Links:

Stump Root: http://forum.xda-developers.com/lg-g3/orig-development/root-stump-root-lg-g3-sprint-verizon-t2850906

IORoot: http://forum.xda-developers.com/showthread.php?t=2776198

However, if I recommend a modded stock ROM.

*** Beyond this point (if you decide to do any of this) if anything should go wrong the developers of the software nor I are responsible. Do everything at your own risk (though it's safe, but had to include this :D).***

Like SkyDragon G3 or Jasmine ROM (I prefer SkyDragon) which will fix a few issues and give you better battery life as performance, as they are just modded stock ROMs. If you do decide to go with this method, the steps are as followed:

• Downgrade to 10b or 11c (I recommend 10b)
• Root with Stump (10B only) or IORoot (10B and 11C) (Stump is WAY easier)
• Install SuperSU (I don't know if you need to with IORoot, but I have only used Stump root)
• Enable Survival Mode
• Install TWRP
• Download SkyDragon G3 (Or Jasmine ROM, whichever you see fit)
• Boot into TWRP
• Install SkyDragon G3 (Or Jasmine ROM, whichever you'd like.)
• (RECOMMENDED) Install 12B Modem
• Wipe Cache/Dalvik
• Reboot
• Enjoy

Links:

How to install TWRP: http://forum.xda-developers.com/verizon-lg-g3/orig-development/bump-unlock-lg-g3-twrp-verizon-t2900590

Updated TWRP (Flash in TWRP after you've unlocked): http://forum.xda-developers.com/verizon-lg-g3/orig-development/recovery-twrp-touch-recovery-2-8-2-0-t2966014

SkyDragon G3: http://forum.xda-developers.com/verizon-lg-g3/development/dec-9-skydragon-g3-vs985-kvt49l-vs98512b-t2967868

Jasmine ROM: http://forum.xda-developers.com/verizon-lg-g3/development/rom-jasminerom-v1-0-t2904641

I was digging around and found a bit more heavily modded (or so it seems) stock ROM called Eclipse G3. Here's a link if you'd like to check that out: http://forum.xda-developers.com/verizon-lg-g3/development/rom-eclipse-g3-v0-2-12b-1-19-15-time-t3007306

12B Modem: https://www.androidfilehost.com/?fid=95832962473400630