Dear @Abdulbaset.Alazhare,
I’m not sure where the 10/6 came from, but that should be sufficient for the IEA Wind 15-MW RWT. A 12P excitation frequency (which should be more than enough range to resolve) for this turbine is 12*7.56/60 = 1.512 Hz, which is less than 10/6 = 1.667 Hz. My guess is 10/6 was used to get a nice round number for DT_High of 0.3 s. As such, you should be able to increase the TurbSim step size to 0.3 s as well.
Best regards,