15 is not too small of a sub fleet for an airline like AA. They operated a similar size A300 fleet for a long time. As long as the aircraft has a niche in the network, it can operate profitably. A333 was on the way out anyway and AA was going to keep A332 for awhile before the downturn so the withdraw from service has nothing to do with the fleet size and everything to do with lack of utilization.

A332 is mainly used for international service (trans Atlantic to be specific) but they are being stored because there is no alternate use... The type does not have enough cargo room to generate revenue to make up the loss of people upstairs like 777, and it is not as flexible/efficient as 787 to be able to use on trans Pacific routes with reduced load/demand.