Our code more or less just tells AdMob "show ad" and "hide ad".
Absolutely everything else, such as loading and displaying the ad, is handled by AdMob.
So if there's any issue with performance, I strongly suspect it is on AdMob's side. It is extremely difficult to imagine how code as simple as our "show ad" command could cause this type of problem. It is far more likely it's to do with displaying the ad, which is handled by AdMob.