The phytochrome-interacting factor-like gene OsPIL15 negatively regulates grain size and 1000-grain weight, but its regulatory effect on rice quality traits is unknown. Here, knock-down, knock-out, and over-expression of OsPIL15 transgenic rice lines were used to investigate the effects of OsPIL15 on rice yield and quality traits. The results showed that knock-down or knock-out of OsPIL15 increased grain length and width, chalkiness, amylose content, glutenin and globulin content, and total protein content but reduced amylopectin content, total starch content, prolamin and albumin content, and gel consistency. Over-expression of OsPIL15 showed the opposite results, except for the reduction of prolamin content. Although OsPIL15 changed the grain size and weight, it had no effect on grain length/width ratio, brown rice rate, and milled rice rate. KEGG pathway enrichment analysis of differentially expressed genes between transgenic lines and wild type showed that OsPIL15 mainly regulated genes related to ribosome, metabolic pathways, and biosynthesis of secondary metabolites. Gene expression analysis showed that RNAi transgenic lines decreased OsCIN2 and OsSUS1 expression and increased OsGBSSI, OsSSI, OsAPGL2, and OsAPGL3 expression level, while over-expression of OsPIL15 increased OsCIN2, OsSUS1, OsSUS6, and OsSSI and decreased OsSSIIa, OsSSIIc, and OsAPGL2 expression level. These results revealed that OsPIL15 plays an important role in rice grain development. In addition to grain shape, OsPIL15 also regulates chalkiness, starch content, protein content, and gel consistency. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11032-022-01311-x.