Hi,
The following should work
Code: run tran(stop=15us, errpreset='conservative, maxstep=1ns)
I would remove the maxstep paramter though. It generally has no impact on simulation results in Spectre other than slow down simulation, if given a very small value. If you are using threshold type functions (cross, deltax, risetime, ... ), Spectre will place timepoints automatically at the crossing points. If you require fixed timesteps for FFT's then use a z domain controlled source, or strobing parameters.
Regards,
John