Catalysis of the reaction: a (9Z,12Z)-octadecadienoyl-containing glycerolipid + 2 Fe(II)- + 2 H+ + O2 = (9Z,12Z,15Z)-octadecatrienoyl-containing glycerolipid + 2 Fe(III)- + 2 H2O.
1-18:1-2-18:2-phosphatidylcholine desaturase activity (SN2-18:3 forming)