Not sure what you are meaning by "My Z-axis Step/unit= 15000 mm/minutes" I am thinking you may mean 15,000 steps per unit and also you then mention IPM so are your native units Imperial or metric?

If 15000 steps per mm then @25KHz kernel will give you a max of 25000/15000 x 60 = 100mm per min

If the 15000 are steps per inch then it would be 100 inch per min, so not sure where you get the 16IPM frrom as it doesnt work out.

Hood