It'll be fine. Both products work well. The S&S is a little more dense, but is also a bit thinner. I used both products throughout my basement remodel (S&S in the ceiling and some interior walls, R15 on exterior walls). Too bad you aren't closer...I have 2 bags of S&S and 1 bag of R15 left over that you could have used.
Around here, I had to special order the stuff. I even called some places around that were supposed to "stock it" based on the Roxul website and the places acted like I had two heads or something. I finally had to order through HD, but they even had no idea that they could get it and I had to provide the vendor, SKU, etc. to get them to find it/order it.