I agree with Glen. You'd be hard pressed to wreck your edge on 15 strokes on diamond unless there was a huge amount of pressure used, way too much paste on the strop or you lifted the spine whilst stropping.

If its only slightly dulled, you may be able to strop your way back to a good edge. Try doing 60 or 70 laps on leather and see if that brings the edge back. If that doesnt do it, you may need to go to a hone.