One correction: 15 players restriction is not an excuse but rule and it depends on the tournament and it's organisers like ICC or ACC ( which includes substitute, backup or replacement).
Rules could be flexible for bilateral series but even they have limitations on squad.
It is a rule being used as an excuse by Agarkar and the rest of the management in this specific case. They have the final say on who is in and out which is why this is a childish excuse to hide their true opinions.
These fools are still trying to push for an Indian all format captain when most feel that it's better to stick to separate captains for different formats at present. Smh!