Ovarian cancer (OC) poses a health burden of women. Long non-coding RNA SNHG15 has been reported to promote OC progression; however, its effect on immune evasion remains unknown. Here, we investigated the effect of SNHG15 on OC cell immune evasion and the underlying mechanism. Cell phenotypes were assessed using cell counting kit-8, colony formation, lactate dehydrogenase cytotoxicity, and enzyme-linked immunosorbent assays. The mechanism was evaluated by dual-luciferase reporter assay, RNA pull-down, RNA immunoprecipitation (RIP), methylated RIP, and RNA stability assay. The role in vivo was analyzed using tumor-bearing mice. The results showed that SNHG15 and PD-L1 levels were increased, while miR-545-3p expression was reduced in OC. SNHG15 was a sponge of miR-545-3p, and PD-L1 was a downstream target of SNHG15. Knockdown of SNHG15 suppressed OC cell proliferation, and enhanced cytotoxicity and pro-inflammatory response of CD8 T cells, whereas miR-545-3p downregulation reversed these cellular behaviors. Moreover, PD-L1 reversed the cell phenotypes induced by miR-545-3p. Additionally, SNHG15 was modified by m5C, which was mediated by NSUN2. Furthermore, SNHG15 knockdown impeded tumor growth in mice. In conclusion, m5C-methylated lncRNA SNHG15 promotes OC progression by accelerating cell proliferation and immune evasion via the miR-545-3p/PD-L1 axis, demonstrating a tumor-promoting function of SNHG15 in OC.