Of course the reason they changed to 15 knots at Costa Rica was too many flights couldn't circle because of those typical low clouds so flight were diverting.
The maximum tailwind acceptable for the A320 is, to my knowledge, 10 knots. That comes from the Airbus FCOM, and it has been demonstrated and approved. One must remember that it can be with normal flight controls or with the so-called "direct law". The flare on this type of aircraft is a very computed matter with electric flight controls, aside from the increased landing distance due to tailwinds. If a company choses to exceed those limitations with that type of aircraft I do not think Airbus would approve, if asked...After that of course, the captain may decide to do what he thinks best in a difficult situation, but it crtainly should not be allowed on a day to day basis. The A320 is not a 737...