Starter Content is something introduced in WordPress 4.7. This is a feature that enables you to create the demo content for your theme from the beginning. In this tutorial you will get some insights in it and learn how to set it for your own WordPress theme.
Are you bored of Twenty Fifteen theme? I must admit that I am. Although it is a great theme, I wanted to find some other alternative with a similar or same layout. AmalieLite is the one I have found pretty similar but also a little bit different.