Time step size??
 

I have an unsteady flow over a cavity. I want to capture lower frequencies of the the oscillations of a cavity. my simulation is taking a lot of time as my time step size now is 10 ^-7. therefore when i perform a fft I am only able to get higher frequencies when plotting sound pressure level vs frequencies. Can i reduce my time step size and still get accurate results?
Mach no-2
first length-0.005.