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As long as the coating is correct, and the simulation uses periodic BCs with plane wave, and runs sufficiently long, the result should be correct. You ca use index monitor to check the structure.
Did you use single wavelength or broadband? single wavelength can be difficult to know if the simulation is correct or wrong. I would suggest that you simulate a broadband source, even though you only need one wavelength. This is because, from the broadband , you will know if the transmission curve is smooth. You can use "wavelength start" to be the wavelength you desire, and use larger "wavelength stop" at source spectrum.
You can also use a time monitor to see if the signal decays completely, or check the log file to see if the simulation reaches its autoshutoff min. Sometimes you may need to reduce the autoshutoff min.
One more note: since the coating is only 15nm thick, and it is spherical, you will need mesh override to resolve the coating. you ca try about 3nm or finer mesh. Make sure the mesh is also an integer fraction of the periodicity, eg, the override mesh size is Period/N where N is an integer.
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