@duchess64 saidI could see 15...Ne4 with 16...f5 (if White plays 16. Qg4) as possibly being even better than 15...Rfc8. But if I have a path to good winning chances that doesn't involve sacrifices or positional compromises, I prefer that to a possibly stronger line that does involve those things (in this case, the weakening of the e5-square by 16...f5, even though Black's position seems more than sound enough to withstand this).
I would be inclined to play 15...Ne4 (as Greenpawn suggested) before Rfc8.
However, if a fairly straightforward forced win for Black after 15...Ne4 16. Qg4 f5 were demonstrated, I might well go for it.