I have gone through your requirement and I'm pretty confident that I can deliver your requirements with utmost quality. If you are willing to proceed further please ping me. So that we can discuss the project requirements in detail.
As you said this app needs to be tested with atleast 15users. I can assure you that more than 20users were signed up as part of my testing. And also can you please what is the mode of signing up? Is there an auto signup option? For example, signup with Facebook, Instagram or Gmail? If so then again this needs to be tested with different third party apps and check whether the login info is also rendering properly or not. Happy to discuss in detail over chat