The two-volume set LNCS 14771 and 14772 constitutes the refereed proceedings of the 15th International Workshop, PQCrypto 2024, held in Oxford, UK, during June 12-14, 2024. The 28 full papers included in these proceedings were carefully reviewed and selected from 76 submissions. They were organized in topical sections as follows: Part I: Applications and protocols; code-based cryptography; group-action-based cryptography; lattice-based cryptography; Part II: Isogeny-Based cryptgraphy; multivariate cryptography; quantum algorithms; transforms and proofs. .