A huge difference between 15 million and 1.5 million. Even from your Wikipedia source, the highest estimate is actually 1.03 million by ORB. Even that is based on a survey of a relatively small number of households in Iraq. The actual reported death numbers is 80 to 87 thousand by Iraq Body Count. The UN estimate is 34 thousand.
Bottom line is when doing propaganda you pulled a number out of somewhere which was totally unrealistic. The total population of Iraq is less than 30 million. If 15 million would die there then there would not be a single un-injured person left in the country.
IMO, the real number is probably close to the Iraq Body Count number, which is a very high number of people dead but not even in the ball park of 15 million.
The other point to note is that these figures include all deaths (both military and civillian) as a result of actions of all sides (actions by both coalition and insurgents) so blaming only US for civillian death when Sunnis anand Shias have been killing each other freely does not seem quite right.
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Here are the yearly IBC civilian death totals[13]](Casualties of the Iraq War - Wikipedia) (as retrieved on Sept. 23, 2007):
YearDatesCivilian deaths11 May 03 - 19 Mar 046332 (not counting 7400 invasion deaths through May 1, 2003)220 Mar 04 - 19 Mar 0511,312320 Mar 05 - 19 Mar 0614,910420 Mar 06 - 16 Mar 0726,540
Concerning the yearly totals IBC states: “All figures are taken from the “maximum” confirmed deaths in the IBC database. However, IBC’s rates and counts will rise over the coming months, as data is still being added to the IBC database for 2006 and other periods covered here.”[13]](Casualties of the Iraq War - Wikipedia)
The IBC released a report detailing the deaths it recorded between March 2003 and March 2005[93]](Casualties of the Iraq War - Wikipedia) in which it recorded 24,865 civilian deaths. The report says the US and its allies were responsible for the largest share (37%) of the 24,865 deaths. The remaining deaths were attributed to anti-occupations forces (9%), crime (36%) and unknown agents (11%). It also lists the primary sources used by the media: mortuaries, medics, Iraqi officials, eyewitnesses, police, relatives, US-Coalition, journalists, NGOs, friends/Associates, other."