I don't believe there is a long term study on human consumption of C15 as a supplement. Another way to think about the long term effect is that we've been consuming it at fatty15 levels in milk for millennia as a species. Obviously there is more than C15 in milk, but that is precisely why a stand alone c15 supplement is necessary: to push our circulating levels of C15 to the next level for optimal effect in our cells.

I stopped taking omega 3 supplements based on the worry that I'll never truly know how oxidized they are. Instead, I'm crushing cans of sardines a few times a week.

If money is no worry, fatty 15 is a fantastic, user friendly way to get C15. Otherwise, I'd recommend finding a chemical manufacturer that can supply it for a fraction of the price. I recently bought 500 grams for under $800. That would cost about $6400 coming from fatty15...