I do not think the 15-miunte time slot necessarily indicates that the firm actually expects the interview to ask for that long. It may be that they only plan to ask 3-4 questions and are accounting for potential 2-3 minute answers, introductions, and potential delays when calculating how much time they should book to make sure one interview does not overlap with the one scheduled next.
As for the questions they could ask, I do not expect they could go much further beyond the following:
- The general motivational ones: probably the why commercial law, why firm, why you are all fair game
- Application strategy questions: what other firms have you applied to, why would you prefer Macfarlanes
- Firm research questions: could be simple ones such as explaining what their main practices areas do or how a current issue impacts them, but also more complex questions around the firm's strategy and market position.
Finally, in terms of preparation advice, I think it is similar to what I would say for most interviews, in that practicing as much as you can and then critically assessing your performance is the right way to go about it. The one point of difference I would mention is that with phone interviews, since your interviewer will not be able to see you and infer anything from body language and expression,
you should focus a lot more on improving the clarity of your oral communication.
