According to the Stockholm International Peace Research Institute, between 2005-2009 and 2010-2014, Russian exports of major weapons increased by 37 percent; Russia spent $66.4 billion on arms in 2015, then $69.2 billion in 2016, having taken 3rd place (after the U.S. and China).  According to the Russian Defence Ministry, share of modern weapons in the Armed Forces reached from 26 to 48 percent among different kinds of troops in December 2014. This was raised to 30.5–70.7% as of July 2015. The average was 58 per cent over the first half of 2017.
Question: How many billion dollars did Russian arms spending increase by from 2015 to 2016?
Answer: 2.8