A plant-based expression system provides a cost-effective, scalable, and safe alternative to traditional cell culture platforms. In this study, recombinant human interleukin-15 (IL-15) was transiently expressed in Nicotiana benthamiana plants using agroinfiltration. IL-15 is a cytokine with significant potential in cell engineering, immunotherapy, and cancer therapy. A codon-optimized IL-15 gene was cloned into a binary vector designed for plant expression and introduced into Rhizobium radiobacter (formerly Agrobacterium tumefaciens). The R. radiobacter for human IL-15 expression was infiltrated into N. benthamiana leaves. Following purification, receptor-binding assays confirmed that the plant-derived IL-15 could bind to the IL-15 receptor comparably to its mammalian-produced counterpart. This first report of IL-15 expression in plants highlights the promise of plant-based systems for biopharmaceutical production and lays the groundwork for further development of IL-15 for applications in cell engineering, clinical therapies, and the cultured meat industry.