As far as I remmeber we never managed to beat any SRB at that time (mine or the ones I joined in). The impossibly short duration made it .... well impossible since it was hard to get enough people participate. Even if everyone was nuking with their best squads (granted our best squads at that time were much weaker than what many of us have now).

If it was 1 Hour duration instead of 15 minutes it would be much plausible, since the amount of HP on the Boss was drastically high for such short time limit.