Refinement is one of the cornerstones of a formal approach to software engineering: the process of developing a more detailed design or implementation from an abstract specification through a sequence of mathematically-based steps that maintain correctness with respect to the original specification. The aim of this BCS FACS Refinement Workshop, is to bring together people who are interested in the development of more concrete designs or executable programs from abstract specifications using formal notations, tool support for formal software development, and practical experience with formal refinement methodologies. The purpose of the workshop is to provide a forum for the exchange of ideas, and discussion of common ground and key differences. This 15th workshop continued a 20 year tradition in refinement workshops run under the auspices of the British Computer Society (BCS) FACS special interest group. After the first seven editions had been held in the UK, in 1998 it was combined with the Australasian Refinement Workshop to form the International Refinement Workshop, hosted at The Australian National University. Six more editions have followed in a variety of locations, all with electronic published proceedings and associated journal special issues.