Reminds me of a fundraiser we'd have at my elementary school every year. We'd release a bunch of balloons with instructions to mail back some details about where they ended up. It was fun to see how far away some of them ended up. But yeah, 1.5 million is crazy and that's a lot of helium we can't get back.
In the early '60s I was a 1st and 2nd grader in what was then West Germany. We had a day each year when we would write messages of friendship that were tied to balloons which we then released in hopes of them floating over the stretch of the Iron Curtain which ran near our base. The idea being that some balloon deprived East German child would realize that Communism wasn't so great. The Wall did come down, so those balloons obviously worked.
...And so began the great toilet paper shortage of '86