If I read your earlier problem correctly you may have a further problem, if you're looking for 1/15,000 to 1/20, 000 of a second with a lot of power. Most shoe or handle bar flash units have a duration of about 1/1000 - 1/2000 at full power, so 1/15000 would be way down on the power scale. Studio strobes could be as slow as 1/750 at full so the only way you might be able to get the duration you want is multiple studio strobes at very low power settings.
Butch
