Long or short intervals for trail race?

HK Pink Lady

Here in Hong Kong the road race season is coming to an end.  I have one more race in 2 weeks, a 15K hilly trail race.  I am wondering if I need to train short intervals (like 200 /400 reps) or longer intervals (mile reps and longer) to prepare.  Any suggestions?  

My last road race was a flat 10K in which I nabbed #3 in W50+, previously a hilly road HM, also #3 W50+; for the 10K I tended to train shorter intervals, 800m and 1000m.