Played against both and spoke to a couple of good guys who have used both extensively.
SLDR is the one if hitting fways might be an issue (see forgiveness / speed). The other one keeps up with the rest a bit more than even the SLDR and the SLDR is no slouch. Downside of the R15 is that forgiveness / speed / maybe higher trajectory in cross winds although never heard anyone mention the latter as an issue. I think most should be fine with the R15..............personal that though, and so no clear just winner IMHO :)