15m/s storms are really not among the worst. Between 20-30m/s, most platforms have to give up. Indeed I am sorry SH3 has 15m/s as the worst storms. I'd have liked to see them worse.
Destroyers in particular - historically at least - did not perform very well in such rough seas as these. My mind drifts toward the battle of the North Cape. Not only did the leader of the German destroyer flotilla long struggle against these waves, dramatically reducing his speed, but admiral Bey on the Scharnhorst could at one point, though damaged, have outsailed the British destroyer, since lighter ships don't fare so well in headwind as heavier ships.
There could probably have been even worse seas than those that are in the game now, and if there were, I'd love to see the crew green-faced!
Reduced efficiency and whatnot.