Fifteenth is a free theme for WordPress created by Brian Harris.
A derivative of the TwentyFifteen theme - Fifteenth is a clean, blog-focused and designed for clarity. Fifteenth takes you back to the original TwentyEleven/TwentyTwelve look and feel while still retaining the charms of TentyFifteen.
(Description "Fifteenth" Theme from wordpress.org)
You can download Fifteenth for free via the provided download link and include it into your themes folder of your WordPress installation. Also you can directly search for it in the WordPress admin interface in the themes section and install and activate it from there.
More information, screenshots and reviews of Fifteenth Theme can be found here.