Unity Admob Implementing Interstitial

In my game I want to show interstitials when someone loses. I had banner ads working great, but then I changed my code to adjust for interstitials, and now it takes a while for my banner ad to show up, and when it does it lags for a second. I also am having trouble figuring out how to get my interstitials to pop up and then request another one. I have an ad manager and the way I am telling my game when to display an ad is when the death screen pops up, then an ad should be displayed, and when the death screen goes away, I want to request another ad. So far, I haven't been able to get it to work. Here is my code: using System.Collections; using System.Collections.Generic; using UnityEngine; using GoogleMobileAds.Api;

 public class AdManager : MonoBehaviour {
 
     //public bool dead;
     public int showAd;
     public InterstitialAd interstitial;
     public BannerView bannerView;
 
     void Start () {
         RequestBanner ();
         showAd = Random.Range (1, 3);
         RequestInterstitial ();
     }
 
     void Awake () {
         DontDestroyOnLoad (this);
     }
 
     void Update () {
     }
 
     void ShowInterstitial () {
         if (GameObject.Find ("Canvas1").GetComponent <Canvas>().enabled) {
             if (showAd == 1) {
                 if (interstitial.IsLoaded ()) {
                     interstitial.Show ();
                     interstitial.Destroy ();
                 }
             }
         }
         if (!GameObject.Find ("Canvas1").GetComponent <Canvas> ().enabled) {
             RequestInterstitial ();
         }
     }
 
     public void RequestInterstitial()
     {
         #if UNITY_EDITOR 
         string adUnitId = "unused";
         #elif UNITY_ANDROID
         string adUnitId = "xxxxxxxxxxxx";
         #elif UNITY_IPHONE
         string adUnitId = "xxxxxxxxxxxx";
         #else
         string adUnitId = "unexpected_platform";
         #endif
 
         // Initialize an InterstitialAd.
         interstitial = new InterstitialAd(adUnitId);
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder()
         .AddTestDevice ("xxxxxxxxxxxx")
         .Build();
         // Load the interstitial with the request.
         interstitial.LoadAd(request);
         }
 
 
     void RequestBanner()
     {
         #if UNITY_EDITOR
         string adUnitId = "unused";
         #elif UNITY_ANDROID
         string adUnitId = "xxxxxxxxxxxxx";
         #elif UNITY_IPHONE
         string adUnitId = "xxxxxxxxxxxxx";
         #else
         string adUnitId = "unexpected_platform";
         #endif
 
         // Create a 320x50 banner at the top of the screen.
         bannerView = new BannerView(adUnitId, AdSize.Banner, AdPosition.Bottom);
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder()   
         //.AddTestDevice(AdRequest.TestDeviceSimulator)       // Simulator.
         .AddTestDevice("xxxxxxxxxxx")  // My test device.
         .Build();
 
         // Load the banner with the request.
         bannerView.LoadAd(request);
     }
 
 
 }