Just installed Sumo Springs on the front of our 2015 E450 Class C Thor Chateau 31W. It seems to done what I was hoping for, although it did raise it by about an inch and a half, our coach also has Hel...
It will be stiffer. How stiff depends on the rate of springs installed. I have them on the rear of my Sprinter based RV and it's stiffer,
After lifting the front that much I would be inclined to get the wheel alignment checked. The E series has a lot of geometry change with vertical wheel movement due to the swing axle suspension and you just moved the static position 1 1/2 inches.