It didn't last 15 minutes. I'd be surprised if it lasted a minute.
Unless you're talking about everything that came afterward as well.
Everybody knew they were going to team up looooooong before the Doomsday reveal. It was in the "Dawn of Justice" subtitle, and just a foregone conclusion in general.
Actually, investigating it was how Lois discovered Luthor's involvement in the incident and how far back he was manipulating events to make Superman look bad and push the conflict along. KGBeast was also present for it, and he showed up throughout the film. Lois's investigation played a part in Luthor being jailed at the end. It was hardly forgotten.
That would have been cool, but marketing Wonder Woman so heavily was a really smart move. People were hyped about her big screen debut. And then there all the people in movie theaters who cheered when she showed up in the trailer. I don't think downplaying her role was ever an option.