One thing to keep in mind is the Paton's is wool and not machine washable. I've used Jiffy on 13s, I think 15s might be too big for it. You can do a sample with them and see how they work out. And I think you mean one row of knit st and one row of purl. Garter is what you get when you knit every row or when you purl every row. When you knit a row and purl a row that makes stockinette and for a scarf or blanket the edges and the ends will curl under. You could do about 4 rows of garter stitch, then start stockinette but keep about 3 stitches on each end in garter st. So knit 4 rows, knit 1 row, next row k3, purl across to the last 3 and knit.