Someone once said, You're not in loss until you sell. And in my experience, That's true. I wouldn't suggest that you sell at a 15% loss unless more downtrend is expected from the coin. To avoid such in the future, Endeavor to place stop losses on your trade. That way, You can skip this part and not worry about selling in loss.
The situation is totally different from what it shown in the past years. Our market trend today is not aggressive as it have. Many we're losing their money and it gives a little bit worries when seeing no market price improvement.
If we keep on holding, nothing to happen. Some coins are continuing to decline, though it's too crazy to sell but we must in order to stop from losing it anymore, otherwise we've got nothing in the end.
Therefore it's necessary to act based on the market condition, since it's bearish now, we should not be aggressive anymore, otherwise we will only loss our money. Go with the flow, not against it, and holding is still the best way to combat the situation, we aim for success so we have to do things in order to achieve our purpose. As if the market before were not able to experience bearish, we've seen it many times so it's nothing new to us.