(The 2015 International Energy Conservation Code was previously adopted.) The electrical (2017 NEC), plumbing (2015 IPC) and fuel-gas (2015 IFGC) codes are adopted at the State level.
This is a big step up from the 2006 codes. The good people at Colorado Code Consulting, LLC, with offices in Denver, Colorado Springs, and Frisco, put together a list of significant changes, between the 2009 and 2015 editions of each code, for the City of Denver. The City of Denver is sharing this resource with other Colorado jurisdictions. Many of you are already familiar with the 2009 I-codes from working in surrounding jurisdictions. These documents (on the building department home page) will be a good place to start in making the transition.
To read the I-Codes visit https://codes.iccsafe.org/public/collections/I-Codes.