I agree, that this post is in the wrong place, because the subject is not a general chat. It needs to be at the Projects, Designs, and Technical Stuff. The general section is for how is the weather at your place, austerity and unemployment rates causing you to suffer or have less things in life, or are the birds chirping at your outside tree bothering you.
The 555 multivibrator oscillator transistor-transistor logic IC is not made to operate in 15 V DC. It cannot give such a high volts peak in the square wave. Op Amps are not meant for such a high volts peak, either. You will need a continuous load, of the amplifier can be ruined. I almost want to suggest a power amplifier, but I have no experience with this. An opto-relay might with used to switch on and off the 15 V from a 15 V DC power supply output. The opto-relay is fast and silent and can take the 5 V square wave signal from the 555 oscillator and switch the output of the 15 V DC power supply that is left continuously on. The 15 V DC output signal needs to be conditioned with a bounce less circuit or capacitor in Don Lancaster TTLogic Cookbook.
There are two ideas, switching the output of 15V DC power supply or input to a power amplifier. Power amplifier requires a continuous load and specific impedance - resistance, otherwise the amplifier will be ruined, blown amp. Why do you have to build this invention?
Lawsen