So hold on 1 minute with these changes...

Old Nautilus with 4 items at level 18(Banshee's Veil, Righteous Glory, Randuin's Omen and Sunfire Cape): (1900*(15/100)) + 300 = 585 Health from Shield.

New Nautilus with the same 4 items at level 18: (3938*(17/100)) + 85 = 669.46 Health from Shield.

So a small buff. Let's say around a 100-120 health buff on the shield.

Seems nice! :)