"In 2014 ...we did take a $300 credit on form 8863 line 19. I think that was the LLC".
Line 19 of form 8863 can be either LLC or AOTC. If there is an entry on line 9 of form 8863 (and line 68 of form 1040 or line 44 of form 1040A) you claimed the AOTC, not the LLC.
Otherwise, you should be good to amend 2015-17. If not, pick the best 2 years to amend. It is too late to amend 2014.
