^^This plus the far better tire compounds, tread design and construction of 17" or 18" over what you can get in 15".
After driving a 66 Coronet 500 with a 440 and 4 wheel, 10" drums (completely new on all 4 and the master) several years in the the rain, snow and heat of Oregon, I'll tell you drums suck. A trip down the Columbia Gorge in a down poor turn braking into a plan a head operation, like start applying brakes about a mile before the exit so they would actual work when you got to the stop sign.
To the OP, call or email Dr. Diff. Cass will set you straight and answer any questions you have, and will support his products after the sale.