This book constitutes the proceedings of the 15th International Conference on Computational Processing of the Portuguese Language, PROPOR 2021, held in Fortaleza, Brazil, in March 2021. The 36 full papers presented together with 4 short papers were carefully reviewed and selected from 88 submissions. They are grouped in topical sections on speech processing; resources and evaluation; natural language processing applications; semantics; natural language processing tasks; and multilinguality.