I learned on a tomahawk, and the C152 conversion took me a little over an hour, if I remember rightly. I always found the C172 a bit harder, but that's partly because except in the very modern ones I can't reach the pedals and see over the cowling without more cushions than is either comfortable or safe.
The C150/152 is a very easy aircraft to fly, but if you learned on low wing aircraft, it will feel a bit different. And you'll need to get used to the fact that in the circuit, as soon as you turn, you can't see where you are!