It's also my understanding that one can have too large a sea-anchor, providing too much anchoring capability at the expense of strain and desirable leeway. I'd anticipate the need for beefing up a bollard or cleat as well. 15 tons of stress either by single part or bridle is a load no matter what.
Please let us know of your on-going experiences, Jim.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.