Simple method is to take a clock ( Cheap single cell wall clock is perfect, and looks of the clock don't matter here) and rip apart the clock mechanism, to get the small PCB with the crystal, divider and clock driver out of it. Make a note of which pads go where. Power it from a 1.5V supply ( a resistor driving a red LED and a 100uF bypass capacitor) and use a single NPN transistor with a 10k base resistor and 10k collector resistor as a level shifter. Gives a simple source of pulses at 2 second intervals, now you just use 2 4017's to divide by 5 and 3 respectively, using the output from 2 ( or 1) from the second divider to trigger a 0.5 second monostable to drive the clock coil. Being a slave clock in a master slave system you probably will need a simple 24V DC supply to drive the coil, which does not need to be regulated, an 18VAC transformer and a bridge with 1000uF/50V capacitor will work fine . Use a 7812 to make 12V for the dividers, and drive the clock from the 12V rail, the LED will double as a power indicator.