Wouldn’t it make sense to look at the speed of light during that epoch to be a rapidly decaying function? Then the mass of the universe isn’t going faster than the speed of light. And 15 billion years later, when mankind is obserfing the speed of light, it has every appearance of being a constant.
Or put another way, photons could not break the speed limit because they didn't exist yet - even though, in retrospect, we can use that measure (speed of light) as a constant to express how quickly the universe expanded in the Big Bang/Inflationary Model.