The $15 discount applies only to the PlayStation 4 and Xbox One versions of the open-world game, not Windows PC. If you want a physical copy, you can still get it in time for Christmas with two-day shipping if you order by about 1:15 p.m. ET today. But the offer is also valid for digital copies on both PS4 and Xbox One.
If you're interested in the Collector's Edition of Just Cause 3, which is available only on PS4 and Xbox One, you can also pick that up at a $15 discount today from Amazon. The deal drops the price from $109.99 to $94.99. That package includes a replica of Rico Rodriguez's grappling hook; a 2-square-foot map of Medici, the game's setting; and a 32-page art book.