Welecome to the site
Basically, upgrading to the 2LT gets you better electronics/"bells & whistles". Upgrading to the 3LT gives you more leather and higher quality materials.
And as long as you do not pick Jet Black interior, 2LT gives you a little more color on the interior and 3LT gives you a lot more color.
I'm ordering Jet Black interior so I am definitely going with a Z51 2LT.