How large should the Leander's marine detachment be?

Why does a ship with thirty-three naval crew need fifteen marines?

A demanding boarding mission could justify them; otherwise the suggested alternative is a smaller specialist team supported by cross-trained sailors.

The fictional Leander carries fifteen marines alongside a ship's company of thirty-three. That is a substantial allocation if the naval crew must operate the ship independently. A strong boarding requirement would help explain it, but the mission needs to justify the proportion. A smaller specialist team supported by trained sailors is suggested as another arrangement. The question is what the marines must do aboard this particular ship, rather than whether every warship needs the same detachment.