How many people should i interview for my project realization?

Question

For my school project I'm realizing some sort of digital touchscreen that can show the full stock of warehouses.

For the usability of the screen and the software that's currently running on it i did like 15 interviews. They've all told me the same thing and that's: Yes, sure i would buy something with this thing. And oh i think this is quite necessary when I'm buying something.

So now: the project is almost finished and it's ready to be put in real stores. I just want to ask the people if they will buy something with my display. For now i've got 5 people.. do you guys think that's enough?

Answer 1

Is it possible to keep the system updated throughout the stores? If yes, launch with the current feedback level. Then you can improve the same based on further feedback.

If the regular change is not possible, then better to get feedback from multiple age groups with different skill level. Also, in that case, launch it in as few stores as possible to gain understanding.

I say this, simply because real life use is pretty different to what surveys suggest. A lot of times, people don't want to add extra layer of complexity in real life, but during surveys they won't consider that as a problem.