Poincare had a brilliant thought experiment about what if everything in the universe doubled in size, would anybody notice any difference or even be able to measure anything that can be compared with previous measurements.
Similarly what if one morning one the great constants in physics; that is the speed of light suddenly increased to 150% of what it was; would there be observable differences?
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.
