I woudln't consider that significant at all, rather, insignificant.
15 ppm = fifteen milligrams per kilogram.
So for every kilogram (2.2 pounds) of walnut hulls, whatever, you get 15 mg, provided the information is correct.
If someone wants to ingest 2 pounds of something to get 15 mg of iodine, that's their choice.
If someone wants to process a source that is only 15 ppm to provide a tincture, concentrate, or whatever, I'd say its a poor business decision since so many other sources abound having higher concentrations.
15ppm is considered significant since it is sufficient for human health. And this does not even include what we get from dietary sources.
And more is not always better. Too much iodine can cause toxicity. Maybe this is why I have seen so many people report adverse effects from using Lugol's. If we want to overload the body with chemicals for the old shotgun approach this is what we have pharmaceuticals for.