AA uses Terminal 3, and BA to BCN uses Terminal 5 at the moment, and the two terminals are a few miles apart. 90 minutes is the minimum connection time, which is do-able and would not bother me but it would be tight for many passengers. Three hours would be more comfortable. That said, BCN was in the past operated out of Terminal 3 rather than Terminal 5, so keep an eye on that. If it does move to T3, then 90 minutes is plenty.