I don't think accessories that vibrate can work at a lower voltage.
The 342 has a string motor, which is a little different than the accessories that vibrate via an electromagnet and fingers.
String motors can be adjusted to run at different voltages depending on the gap between the electromagnet and the vibrating armature. I suspect that the gap on DM's 342 is larger than smaller.
Also how far the line tension spring is extended.
That written, it can be tricky to make those adjustments. If the instructions say 15 volts, and the accessory works properly at that voltage, I think that I would recommend that a person who does not have a lot of experience with those mechanisms try to make an adjustment.