Is an opto-coupler fast enough for this application?
No, this will not work with the 10kohm load resistor.
Look at datasheet diagram 13, at 10kohm load resistor, it takes about 50us for the signal rising edge to propagate from input to output, while falling edge propagation is below 2us.
As 75kHz is about 13us period, you need signal rising edge propagation time much faster than that, and you can go down to 10us with about 470 ohm resistor.
If this resistance is too low, then you need another optocoupler.