You're wrong. This is the first mass-shooting of 2015 in the state of Colorado. There have been 344 mass-shootings thus far in 2015 in the United States.
There was also only 1 mass shooting in Colorado in 2014 (out of 336 nationally), and 4 of 363 mass shootings in 2013 were in Colorado.
Source:
http://shootingtracker.com/wiki/Mass_Shootings_in_2015
shootingtracker defines a mass shooting as "four or more people are shot [not necessarily killed] in a spree or setting, likely without a cooling off period. This may include the gunman himself ... or police shootings of civilians around the gunman."