The E sedans , non amg models should always be under 1% I believe. When you get into the coupes and especially the convertibles, that becomes tougher on current year model (1 year old model, definitely can hit under 1%).
Most of the great deals on this forum for e300’s have been for demos. @Tourist 10% off MSRP is pretty much what I have been quoted by multiple dealers as well for a brand new 2018 e300. Is a 15% discount on a new model realistic?