Power line protection: overvoltage, ESD, voltage polarity
It won't work because D1 and D2 are always reverse biased - try swapping them around.


  Can this set up secure the system from all kinds of wrong voltage
  inputs?


No, of course not but you could help matters by fusing the lines so that the zener diodes are protected from an overcurrent. You could also think about using crowbar methods to prevent zeners from overheating on marginal over-voltages. Crowbar circuit: -




  What shall be the clamping voltage of the zener diode? Shall it be
  around +15V?


This depends entirely on what voltages your control board can permanently survive.