Looks like the interrupt pins are defined in the pinsmux.h file in the variants directory for the board.
Based on that the pins can be used for interrupts:
0, 1, 2, 3, 8, 12, 13, 15, 16, 17, 18 and 19.
I did test all of those pins using a encoder (one side only). All worked to count except D15 was counting even if I didn't turn the encoder so maybe something was active.