What's funny is I just switched from DALVIK to ART. Not only is my phone SIGNIFICANTLY snappier now, but Facebook is now working flawlessly.
For those looking to eliminate all lag:
1) Go to Settings / Developer Options / Select Runtime then select "Use ART" and approve the change. The phone will reboot and optimize your apps (which takes a few minutes) but it's well worth it.
2) Go to Settings / Developer Options and change "Window animation scale", "Transition animation scale" and "Animator duration scale" all down from 1x to .5x
After doing both of these my G3 now feels as snappy as my completely optimized Nexus 5 was.
LG G3 (D851)
Nexus 5 // Nexus 4 // Galaxy Nexus // Nexus One