You need to set up one of your HIGH priority interrupts with a port bit that gets set during its routine and cleared at the end of it. Then set up another port bit (different) for the LOW priority interrupt and set it on entry and clear it on exit. Then take a scope and look at both bits during operation and see if the LOW priority is interrupted by the high priority interrupt, it should be.....
I would not bother , if you look at the INT_CREATE macro it only creates high priority interrupts


Code:
;---[Stay compatible with the 14-bit version]---------------------------------
INT_CREATE macro
INT_CREATE_H
endm
ENDASM
dave is correct , to use h and low priority interrupts you must use INT_CREATE_L and use
INCLUDE "C:\PBP\INCLUDES\ReEnterPBP-18LP.bas" ; Include if using Low Pr. PBP INTS