I don't think it's fair to cite numbers from 2012 in regards to terrorism as to why 2015 is the safest year. I get the numbers aren't available, but in 2012, Al-Qaeda was weak, Daesh was just beginning, and no one even knew of Boko Haram and Al-Shabab. I think it's pretty fair to say 2015 has been the worst year for terrorism in a really long time. Suicide bombings regularly in Syria and Iraq, executions of civilians and religious minorities, planes blowing up, France essentially on lock down even a month after the most deadly attack on French soil since WWII, thousands of children kidnapped in Nigeria, I certainly don't feel safer in regards to terrorism now than I did a few year ago.
I think it's a joke they cite the Iran Nuclear deal as a reason considering they've already violated it.
I agree with many things in the article though and definitively think post 2000 is the best time to be alive ever.