That's why it really depends on how you look at your lost. Going back to 15% lose, I would say that its not a good thing to sell because we all know that the market is very volatile and a swing of 15% regain is very common. So it really depends on a lot of factor specially how you look at your investments, whether short or long, just saying.
Disastrous for those going short. 15% is painful already, what more for an 80% negative. Though i doubt many could've expected how the market plunged to these levels recently. Most of us are expecting a recovery instead of this.
I am one of those people who suffered almost that big loss. I bought at the beginning of the year and the price then bled, many people suggested to hold because it was only a correction. but prices continued to weaken. my assets decreased by more than 50% and there was no choice but to cutlose and hope can buy again at the bottom line
There are many other investors who experience big loss until now. Even me I experience it before , Having a huge loss is a big frustration for me. I have other coin that take a deep price , The only thing I do is to hold it and start waiting for a good news.