Welcome to the board!
15 broken needles is a lot! How does the Juki work off the frame? It sounds to me like there is a problem with the machine.
Off the frame, does the needle graze the stitch plate? What size and type of needle are you using? Is the needle seating correctly into the needle bar? Are the needles breaking at a specific point in the quilting (in tight loops, always when you head northwest, etc.), or is it random?
I'm sorry you're having so much trouble... You might have to take the Juki back to the dealer and have them look at it. This is not good behaviour for a new machine!