though the my next step is to have this trigger as interrupt to control the latch while performing another routine
It might be a lot less complicated to just increase the osc speed from 4MHz and clock the SPI faster. Running at 32MHz with SPICLK=8MHz it takes <2us to send out a byte... hardly worth the bother. At the speed you're running now it takes longer than that just to branch to an interrupt.

I'd also ditch the PAUSE in the Send_Data routine.