By being very small. 15k rpm is 250 hertz. This is slightly lower than the lower bound wing frequency of a female mosquito, which can hover using approximately

By being very small. 15k rpm is 250 hertz. This is slightly lower than the lower bound wing frequency of a female mosquito, which can hover using approximately 100 μW - a tenth the power of this drone. Citations: https://humbug.ox.ac.uk/sound https://humbug.ox.ac.uk/sound https://pubs.aip.org/aip/pof/article-abstract/36/2/021907/3263681/Power-requirements-in-hovering-flight-of https://pubs.aip.org/aip/pof/article-abstract/36/2/021907/32... https://www.dupagehealth.org/DocumentCenter/View/147/10-Things-You-Should-Know-About-Mosquitoes-PDF https://www.dupagehealth.org/DocumentCenter/View/147/10-Thin...