I think in every type of research and work you can always do more to get to a better and better result. 10 is of course arbitrary. I bet by 3–4 conversations, maybe even after just 1–2'structured this way, you will find enough in the stories to start deriving patterns. Once you have a few patterns you think are important, you then need to go back and plan out what features and changes you want to make based on what you have learned.

If by 10 conversations you really don’t feel like you have a handle on things, keep going. But in that case I would question whether you are asking the right questions, or whether you need to even further target who you are interviewing.