Quaternium-15 is a chemical compound that is the nitro-bromo derivative of dioxane.

Chemical name Methenamine 3-chloroallylochloride

Safety
https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_077.pdf

What it is used for and where
Cosmetics
Antimicrobial agent. This ingredient is able to suppress or inhibit the growth and replication of a broad spectrum of microorganisms such as bacteria, fungi and viruses by making the stratum corneum temporarily bactericidal and fungicidal.

Preservative. Any product containing organic, inorganic compounds, water, needs to be preserved from microbial contamination. Preservatives act against the development of harmful microorganisms and against oxidation of the product.
Synonyms: EC number 223-805-0

CAS: 4080-31-3