1) In view of the fact that we know how to measure the speed of light, it follows that a change in the speed of light would be detectable.
2) Any change in the speed of light would have to be accompanied by either a change in $\mu_0$, a change in $\epsilon_0$, or (far more drastically) a failure of Maxwell's equations, any of which would be easy to detect directly.
3) As for universes "like ours" where the speed of light is 150% greater, much depends on what meaning you attach to the phrase "like ours". It's easy to write down a simple Universe --- say Minkowski spacetime with a different constant in the metric --- in which the speed of light is anything you want it to be. If you want a Universe that is more like ours in more exquisite detail, then everything depends on which details you care about. Obviously it can't be exactly like ours.