Thanks for the feedback, but we'd like to reiterate a few key points here just so we are on the same page. Normally WebViews are themselves expensive without the additional CSS and JavaScript of the creatives. If you feel an abnormally big amount of resources is being consumed, you could temporarily halt the operations of these WebViews either via onPause() or
pauseTimers(). Speaking of the creatives, while the SDK does not have controls of the properties of these creatives per se (e.g. size and animation), you have the choice of ad networks from which to request for ads. If you use a web proxy tool, like
Charles, you should be able to tell where a creative comes from (if not AdMob, and if mediation is enabled). You can then disable that network from serving. Keep in mind that the SDK itself is pretty lightweight, but the interstitials can be heavy, especially so with video interstitials. The 28 MB would seem to be coming from the size of the creative itself.
Speaking of the leak, are you able to obtain and provide us a trace that shows the leak? Over time, as more and more interstitials are processed, the SDK will perform internal memory cleanups automatically to stabilize the memory, so seeing memory usages spiked long-term would be abnormal.