"Sixteenth, seventeenth, eighteenth, nineteenth"
Translation:dek-sesa, dek-sepa, dek-oka, dek-naŭa
Please remember, that since the fraction is of the whole number dek ses, it has to be written as one word deksesono (or with a dash, which is always optional). ;)
It's an important distinction with more than one fraction, since e.g. dek sesonoj means 10 ⋅ ¹⁄₆, while deksesonoj means an unspecified number of fractions ¹⁄₁₆.