Memorising can be a good strategy for speaking part 2 because the same topics are often repeated. Click here to see the six main topic areas that I tell my students to prepare first.
But memorising can be a risky strategy unless you are able to adapt your answers to the specific question. For example, if you prepared a description of a holiday, would you be able to adapt it for this question about a positive experience you had as a teenager?
The smart way to study for part 2 is to prepare a few key topics, then spend lots of time practising ways to adapt what you prepared to other questions.