That is correct - 16. That assumes that MKD and Mansfield both win all their remaining games prior to the final day.
I have been playing with a few permutations: apologies if these are wrong, I am no mathematician.
a) If Lincoln beat Mansfield or MK Dons, it falls to 15 (i.e. 12 more in addition to the three points from that win).
b) If Lincoln beat both Mansfield and MK Dons, it falls to 13 (i.e. 7 more in addition to the six points from those two wins).
In other words, we need five wins and a draw - 91 points - to be certain (or four wins and four draws).
Or five wins provided one of them is either Mansfield or MK Dons - 90 points (or four wins and three draws).
Or four wins and one draw provided we beat both Mansfield and MK Dons - 88 points (or three wins and four draws).
Those requirements tumble with every game MKD and Mansfield fail to win.