Michelle Obama’s Becoming is selling at a pace rarely seen for a political memoir or any non-fiction book.

Combined hardcover, e-book and audio sales in the US and Canada topped two million copies in the first 15 days, Crown Publishing said. By comparison, former first lady Hillary Clinton’s memoir Living History needed a month to sell one million copies.

Former president George W Bush’s Decision Points took several weeks to reach two million. Ex-president Bill Clinton’s My Life quickly sold one million copies but took far longer to hit two million. Becoming, which came out on November 13, now has 3.4 million hardcover copies in print.

The former first lady is in the midst of a promotional tour, with guests including Oprah Winfrey and Reese Witherspoon.