I need to make a function that sets a cell to current time +15 minutes

function firstbreak() { 
   var sheet = SpreadsheetApp.getActiveSheet();
   sheet.getRange(1,3).setValue(new Date).setNumberFormat("h:mm AM/PM")

}

I have the function working properly to set the cell to current time. How can I get the function to set the cell to current time +15 minutes?

I suggest

function firstbreak() { 
  var sheet = SpreadsheetApp.getActiveSheet();
  var now = new Date();
  var fifteenMinutesLater = new Date(now.getTime() + (15 * 60 * 1000));
  sheet.getRange(1, 3).setValue(fifteenMinutesLater).setNumberFormat("h:mm AM/PM");
}