Compound fertilizer 15-15-15 refers to a compound fertilizer with a nitrogen, phosphorus, and potassium content of 15% and a total content of 45%. Nitrogen fertilizer can promote tree growth and supplement nutrients for plant growth; Phosphate fertilizer can promote flower bud formation, flowering, and early fruit ripening; Potassium fertilizer can promote the strength of stems and improve the plant's ability to resist diseases, pests, drought, and lodging.