I loved the 15th sprocket everywhere except the interstate. As Blacktiger says, the mpg suffers. I was getting 30mpg loaded down going 80-90mph. I put the 16th back on because I get on the interstate all the time.
IMHO, the best thing to do is use a 17th to travel somewhere (Moab) & install a 15th when you get there.
Heart of Dixie