Interstitial ad with delayed loading

Question

I’m trying to implement an interstitial ad, and I would like it to be loaded before, in the app it’s happening to load along with the action which causes delay and makes the ad appear well after. I want to make the ad appear right after pressing "add" as shown in the image below:

The code below shows how it was implemented:

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        mInterstitialAd = new InterstitialAd(this);
        mInterstitialAd.setAdUnitId("ca-app-pub-8920922366585510/4181958830");
        mInterstitialAd.loadAd(new AdRequest.Builder().build());
        if (requestCode == ADD_PACK) {
            if (resultCode == Activity.RESULT_CANCELED) {
                if (data != null) {
                    final String validationError = data.getStringExtra("validation_error");
                    if (validationError != null) {
                        if (BuildConfig.DEBUG) {
                            //validation error should be shown to developer only, not users.
                            MessageDialogFragment.newInstance(R.string.title_validation_error, validationError).show(getSupportFragmentManager(), "validation error");
                        }
                        Log.e(TAG, "Validation failed:" + validationError);
                    }
                } else {
                    new StickerPackNotAddedMessageFragment().show(getSupportFragmentManager(), "sticker_pack_not_added");
                }
            }
        }
        mInterstitialAd.setAdListener(new AdListener() {
            @Override
            public void onAdLoaded()  {
                mInterstitialAd.show();
            }
        });
    }

I’ve tried to place the charging call before those codes but I can’t get it to charge before.

            mInterstitialAd = new InterstitialAd(this);
            mInterstitialAd.setAdUnitId("ca-app-pub-8920922366585510/4181958830");
            mInterstitialAd.loadAd(new AdRequest.Builder().build());

The application is an open source github, the link is just below if you want to download to see the full code and help: DOWNLOAD FULL CODE