omega(3) desaturase that uses both 18-carbon and 20-carbon n-6 polyunsaturated fatty acids as substrates. a (9Z,12Z)-octadecadienoyl-containing glycerolipid + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = (9Z,12Z,15Z)-octadecatrienoyl-containing glycerolipid + 2 Fe(III)-[cytochrome b5] + 2 H2O Lipid metabolism; polyunsaturated fatty acid biosynthesis. The histidine box domains may contain the active site and/or be involved in metal ion binding. Belongs to the fatty acid desaturase type 1 family.