Most landed I ever pulled was 12 in an A6M5b, but I don't use rearms. That is such an outlier from my next highest that I can only say I was 1) lucky and 2) flying far above my normal skill level, particularly in terms of shooting accuracy. Next highest for me is only 8, which I did once each in the Mosquito Mk VI, P-38L, Typhoon Mk Ib and N1K2-J.
17 is well believable to me to someone using an Me262 who, unlike me, can actually shoot things with it.