A novel soybean variety, designated XB12J15R is provided. Also provided are the seeds of soybean variety XB12J15R, cells from soybean variety XB12J15R, plants of soybean XB12J15R, and plant parts of soybean variety XB12J15R. Methods provided include producing a soybean plant by crossing soybean variety XB12J15R with another soybean plant, methods for introgressing a transgenic trait, a mutant trait, and/or a native trait into soybean variety XB12J15R, methods for producing other soybean varieties or plant parts derived from soybean variety XB12J15R, and methods of characterizing soybean variety XB12J15R. Soybean seed, cells, plants, germplasm, breeding lines, varieties, and plant parts produced by these methods and/or derived from soybean variety XB12J15R are further provided.
