This coin just cannot catch a break. Everytime the overall marketcap takes a dump, nem sheds more sats. It just can't seem to gain any ground with the market being the way it is. It's pretty disappointing. I know many of the others are losing ground as well, but nem is the only one outside the top 10 and down at #15 now.
I think you should sell now, since NEM can definitely go down more, and so can the market. If your timeframe is few weeks to a few months, NEM is unlikely to deliver for you day in and day out, and it also comes with higher volatility as you rightly pointed out.
Just make sure not to come back to the thread in the next bull run about how you missed out to big gains or what not.