A 24-year-old man was sentenced Friday to 15 years in prison for fatally shooting a 17-year-old outside a Walmart in La Habra nearly three years ago. Joshua Christopher Brooks pleaded guilty May 1 to voluntary manslaughter and robbery and admitted sentencing enhancements for the personal use of a gun and committing a crime while out on bail. Brooks had credit for 1,163 days behind bars, nearly 3 1/4 years, according to court records. As part of …