The North Carolina Symphony launches its 2015 Rex Healthcare Summerfest Series at Cary’s Booth Amphitheatre on Saturday, May 23, at 7:30 p.m., with a concert program that features pianist Timo Andres performing Gershwin’s incomparable Rhapsody in Blue, the orchestra’s performance of Dvořák’s New World Symphony, and other works by Copland and Sousa that feature “citizen musicians” as they join the orchestra.