[bies]

MiG-17 was a mainstay of North Vietnamese air force so considering relatively low amount of work to modify MiG-15bis it would be valuable plane.
"Although 13 of North Vietnam's flying aces attained their status while flying the MiG-21 (cf. three in the MiG-17), many VPAF pilots preferred the MiG-17 because the high wing loading of the MiG-21 made it relatively less maneuverable and the lighter framed canopy of the MiG-17 gave better visibility."