Protein N-lysine methyltransferase that specifically trimethylates 'Lys-315' of VCP/p97; this modification may decrease VCP ATPase activity. {ECO:0000269|PubMed:22948820, ECO:0000269|PubMed:23349634}. This is the function of VCPKMT (valosin containing protein lysine methyltransferase, ENSG00000100483).