Does a function evaulation error of (5.95853e-15 ) is not enough for the solution to be correct?
Only you can know the answer to that. How close to the ideal solution do you need to be? And how sensitive is your equation function f(x) to deviations from the ideal solution.
Consider, for example, the simplest equation
The ideal solution to this is x=1, but x=2 provides a solution with error of only f(x)=1e-15. Is x=2 close enough?
Now consider an equivalent equation
Here again, the solution is x=1, but x=2 provides a much bigger error, f(x)=1. Again, does f(x) tell you it is close enough, or still too far away?