Fresh from our rundown of key pieces to own in 2015, we turn to three brands that will define the year to come. Kicking off the second half of the decade with a distinctly retro vibe, we think 2015 will be defined by the casual favorites of the '80s and '90s, as sportswear gets redefined with fashion in mind. With big new lines from Kappa, Fila and Ellesse on the horizon, it's time to get your tracksuit on.