Rotation to joytick direction is so sudden

I have a character rotation to where joystick faces:
Code

void Update () {
	if (Input.GetKey (KeyCode.Mouse0)) {
		x = Mathf.MoveTowards(x,Input.GetAxisRaw ("Horizontal"),(0.1f*tank.manoeuvre)*Time.deltaTime);
		y = Mathf.MoveTowards(y,Input.GetAxisRaw ("Vertical"), (0.1f * tank.manoeuvre) * Time.deltaTime);
	}

	transform.eulerAngles = new Vector3(transform.eulerAngles.x, 0, Mathf.Atan2(x, -y) * Mathf.Rad2Deg);

    if(Input.GetButton("Move"))
	GetComponent<.velocity=-transform.up*tank.speed;
    else
    {
        GetComponent<Rigidbody2D>().velocity = Vector2.Lerp(GetComponent<Rigidbody2D>().velocity, Vector2.zero, 4f * Time.deltaTime);
    }
}

It works when I move the joystick slowly. But when I move the joystick to its reverse (from horizontal1.0, to horizontal-1.0 ) the rotation happens so immediate. I want to make it rotate where the joystick faces, but with a fixed speed.
how can I make it?
Thanks

Instead of interpolating single floats and then putting them into a rotation vector, get a target rotation and interpolate towards that. It’s way less complicated (thus less likely to produce errors) and your speed will be handled more correctly.

var input = new Vector3(Input.GetAxisRaw("Horizontal"), 0, Input.GetAxisRaw("Vertical"));
if(input != Vector3.zero) // Check this because Quaternion.LookDirection doesn't like zero vectors
{
  var targetRotation = Quaternion.LookDirection(input);
  transform.localRotation = Quaternion.RotateTowards(transform.LocalRotation, targetRotation, speed * Time.deltaTime);
}