Two very quick 36" Whiplashes in our club run 1527/1.5Ds on 6S. They are actually pretty good on the batteries because the boats run quite light (both 1P setups, but our races are slightly shorter than yours).
As a comparison, I have run both a 1717 and a 1527/1.5D in my 37" DF 21 MkII mono, and there's barely any difference. I would go fo the 1717.