Make a 360° rotation on demand

Hi I'm having trouble with my script when I try to make the rotation faster. With this script I want, when I click on 'a', to rotate an object by 360°, and reverse direction when I click on 'z' , with this script everything is working well as long as the rotation is not too fast. But I need to make the rotation faster. Does anyone have a solution for this issue ? It would help me a lot.
Thank you guys in advance !

The code :

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class RotationScript : MonoBehaviour
6. {
7.  
8.     private Quaternion Quaternion_Rotate_From;
9.     private Quaternion Quaternion_Rotate_To;
10.     private int pos1;
11.     private int pos2;
12.     static float T = 0.0f;
13.  
14.     void Start()
15.     {
16.         pos1 = 0;
17.         pos2 = 0;
18.     }
19.  
20.     void Update()
21.     {
22.         if (Input.GetKeyDown("a"))
23.         {
24.             pos1 = 0;
25.             pos2 = 360;
26.             T = 0.0f;
27.             Quaternion_Rotate_From = Quaternion.Euler(80, 0, 0);
28.         }
29.  
30.         if (Input.GetKeyDown("z"))
31.         {
32.             pos1 = 0;
33.             pos2 = -360;
34.             T = 0.0f;
35.             Quaternion_Rotate_From = Quaternion.Euler(-80, 0, 0);
36.         }
37.         T += Time.deltaTime * 0.5f;
38.         Quaternion_Rotate_From = transform.rotation;
39.         Quaternion_Rotate_To = Quaternion.Euler(Mathf.Lerp(pos1, pos2, T), 0, 0);
40.         transform.rotation = Quaternion.Lerp(Quaternion_Rotate_From, Quaternion_Rotate_To, Time.deltaTime * 5);
41.  
42.     }
43. }