Yes, Spell Resistance items should be updated to their new values with this preview.
It's actually -10 for legendary saves, plus the additional -6 across the board for a total of -16. Please note the top part of the post, which makes special care to say "These sections are additive - if a monster is in a Legendary Tier 2 dungeon, it will have all 3 sets of modifications as it is level 20+, level 30+, and in a Legendary Tier 2 dungeon."