You have set the lower limit to 15000Hz, and upper limit to 0 (no limit), so what you get is the lowest octave harmonic above the lower limit (15000), and that is, precisely 19230.72Hz. So all is correct.
If you turn on the tool tips and hover over the limits edit boxes you will see the logic is reversed.
> relates to the Maximum output frequency and < the minimum.
I think the symbols would be better on the rhs of the pair of edit boxes myself, or words min/max could be used.
For more details, please check the link: