A 9lb Danforth (aka the old 8S Danforth) is massive for a 15' boat in soft sand bottoms. A 14lb (aka the old 13S Danforth) will hold a 15'r in 100+ mph hurricanes easily...and probably rip the cleats off before dragging. This may help the perspective...I cruised the Bahamas several years on a 28' x 10,000lb ketch and used 13 standards as working anchors. We typically anchored in sand or 6" high grass and used 8' of chain with 1/2 nylon rodes. We experienced near hurricane winds in open anchorages and the 13 standards never moved an inch. The storm anchor was a 22lb standard Danforth. I also used 22lb standards for working anchors on a 42' x 24,000lb cutter and a 40lb standard for storms. All used in hard or soft sand and grass. The downside of Danforths is you can trip them if the tide or wind changes. I don't own an M15 but thinking for anchors would be two 9lb Danforths, 4'-6' of chain and 3/8" diameter nylon for working anchors. Storm anchor would be a 14S. If you go with a CQR be sure it is the right bottom. I've owned and used them on sand and grass. If they hit a submerged shell or rock it can point the anchor up and make it plow out of the bottom and drag. I saw this more than a few times in the Bahamas and not uncommon. I equate a 25lb plow and 25' of chain as almost equal to a 14lb Danforth and 8' of chain in sandy/grassy bottoms. Bill P.