Refers to a historic mixed martial arts event (DREAM.15) from 2010. You may find fight footage on YouTube, but it is not a game. Quick Gameplay Guide (Puzzle)

If you downloaded the puzzle game, the goal is to slide the 15 tiles within the 4x4 grid until they are in numerical order from left to right, top to bottom.

Focus on completing the top row first (1, 2, 3, 4), then the second row. It is usually easiest to solve the bottom-right corner last.

Were you looking for the specifically, or a different "Dream 15" related to fantasy sports or poker ? Dream 15 - Apps on Google Play

If the puzzle game isn't what you meant, you might be looking for one of these:

A specific live poker tournament series. It is not a downloadable video game but rather a series of professional events.