>murder all men above the age of 15 for refusing their demands to convert to Islam
A better plan may have been to humor the islamosickos and then hook up with an army to wipe out these muslim scum. The effort to eliminate islam terror should have been sustained until it completed the mission.
You need to look up the word "Dhimmi"
This was 5 centuries ago. There were only about 500 of the men in Otranto and they withstood a seige for about 2 weeks, giving the King of Naples time to assemble a force.