Jakob Nielsen says even 14 may be too many.
"Elaborate usability tests are a waste of resources. The best results come from testing no more than 5 users and running as many small tests as you can afford."
However, you will always want to, and be told to, seek more information. I, you, and all other human beings, are subject to many cognitive biases which promote gathering as much information as possible, even when that information ultimately adds little to no value -- biases such as the Illusion of validity -- the belief that more acquired information generates additional relevant data for predictions, even when it evidently does not.