It’s a decent discount, nothing special. Currently you are getting ~14%, but you can push for 15% before any incentives and ask for free pre-paid maintenance. Also, price shop with bridgewater (NJ)/ Mercedes of Manhattan/ Mercedes-Benz of Wilkes-Barre (PA) to see the lowest they can come down to. I’ve seen them giving great number when you push them.
Check this link to see if you qualify for fleet/ any other incentives: Mercedes Fleet Discount / Other Incentives WIKI