AND NOW FOR A WALL OF MALL ITEM: MCA Records' new pop songstress is 15 years old, goes by one name (Tiffany) and just finished her sophomore year at Norwalk's Leffingwell Christian High. So when the label decided to send Tiffany out on tour this summer, they wanted her to play arenas where she'd feel right at home. Welcome to the Tiffany Shopping Mall Tour '87. In what sounds like a first (not to mention a savvy marketing ploy), Tiffany will open a three-month concert tour June 23 at the Bergen Mall in Paramus, N.J. Using a specially constructed stage, the Norwalk-based crooner will perform live--with backing tapes--at such suburban hot spots as Cleveland's Great Northern Mall, Chicago's Woodfield Mall, Minneapolis' Southdale Mall and Denver's Southwest Plaza (a Los Angeles date is still in the works). Tiffany's self-titled debut album, which features the new single "Danny," will hit the stores at the end of the month.