Twenty Fifteen WordPress Theme, Copyright 2014-2015 WordPress.org & Automattic.com
Twenty Fifteen is distributed under the terms of the GNU GPL

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

Twenty Fifteen Theme bundles the following third-party resources:

HTML5 Shiv v3.7.0, Copyright 2014 Alexander Farkas
Licenses: MIT/GPL2
Source: https://github.com/aFarkas/html5shiv

Genericons icon font, Copyright 2013-2015 Automattic.com
License: GNU GPL, Version 2 (or later)
Source: http://www.genericons.com