Clinton is right in her broader point that Obama's plan does not include a mandate for people to have health insurance, as hers does. He believes his plan would lower health care costs enough that most of the 47 million Americans without coverage would be able to find a plan they could afford.
But with no mandate, some people would inevitably go without coverage. But how many? Clinton says 15 million; health care experts it's impossible to come up with a reliable number without more details on Obama's plan.
Clinton's 15 million number could be a reasonable estimate -- it's 30 percent of those currently without insurance -- but it's at best a guess. For that we reason, we rate her claim half true.