It depends on what someone considers a long time, because 15 years seems like a long time, although for such a crime it is definitely not a lot. What no one mentions (and it's written in the article) is that after 50% of his sentence is served, DK will have the opportunity to request to be transferred to South Korea, that's part of the plea agreement. I don't know what the laws are there, so it's possible he could get more than 15 years in prison in total, or less if he gets transferred after 7.5 years and they give him less than the second half of the sentence there.