Why Britain preferred larger twin guns to an all-triple Iron Duke

Was an Iron Duke-based ship with five triple 13.5-inch turrets and fifteen guns considered?

No. British designers are described as preferring the next larger gun in a twin turret for simpler maintenance, turning toward triples when useful gun size approached its practical limit.

The proposed fifteen-gun version of Iron Duke is rejected. British practice is described as favouring a larger gun in a twin mounting because twins were simpler to maintain. Interest in triple turrets grew when designs reached guns around 16.5 to 18 inches. Studies of still larger guns are said to have found inadequate rates of fire and limited practical value. In that explanation, triples become attractive once increasing individual gun size stops delivering a useful weapon.