Interesting. I wonder if that 1.5 million is a true figure. I Googled:
Number of Muslims in the U.S.
Nobody knows.
This is a political hot-potato. Some non-Muslims have accused Muslims of exaggerated their numbers in order to obtain more political clout. Some Muslims have accused non-Muslims of releasing false, low numbers in order to "marginalize" Islam. 4 In religion, as in war, truth is often the first casualty.
Estimates of the number of Muslims in North America range from a little over one million adults to seven million adults and children. One cause of the disagreement appears to be related to the percentage of Muslim immigrants:
Who have abandoned Islam since they arrived in the US, or
Who still consider themselves to be Muslims, but who do not participate in mosque activities.
http://www.religioustolerance.org/isl_numb.htm
I got my number from adherents.com - here is a bit more depth:
Islam. In recent years Muslim leaders in the United States have optimistically estimated that there were approximately 6.5 million Muslims in the country (Aly Abuzaakouk, American Muslim Council, 1999). In 1998 a Pakistani newspaper even reported that there were 12 million Muslims in the United States (4.2% of the total population)! After the events of September 11, 2001, many newspaper accounts included an estimate of 8 million American Muslims. This would equate to 3% of the U.S. population, or roughly 1 in every 33 people in the country. No comparable figure has ever been confirmed by independent research similar to the Kosmin or Glenmary studies, or the Gallup, Harris, Pew, Barna polls. Currently, surveys consistently report less than 1% of people surveyed identify themselves as Muslims. Muslim community leaders say that many American Muslims are relatively recent immigrants who either do not have telephone service, do not participate in surveys or are afraid to identify themselves as Muslims for fear of anti-Muslim discrimination. Researchers generally agree that the estimate of 300,000 Muslims in the Kosmin study (1990) and Kosmin's adjusted estimate (to 500,000) are too small to reflect current (year 2005) numbers of American Muslims. In 2004 the National Study of Youth and Religion conducted by the University of North Carolina at Chapel Hill (sample size: 3,370 teens nationwide) found that less than one half of one percent (0.5%) of American teens were Muslim, a proportion right in line with the adult Muslim population, based on other studies. Tom W. Smith of the National Opinion Research Center (NORC) at the University of Chicago is a nationally recognized expert in survey research specializing in the study of social change and survey methodology. Smith published "Estimating the Muslim Population in the United States" in 2001. This is probably the most thorough academic study of this topic in recent years. This study concluded: "The best, adjusted, survey-based estimates put the adult Muslim population in 2000 at 0.67 percent or 1,401,000, and the total Muslim population at 1,886,000. Even if high-side estimates based on local surveys, figures from mosques, and ancestry and immigration statistics are given more weight than the survey-based numbers, it is hard to accept estimates that Muslims are greater than 1 percent of the population (2,090,000 adults or 2,814,000 total)."
I remember reading a Gallup Org poll which stated that at the time there were 2.8 million muzzies in the USA. I believe those were 2003 stats. I cant remember the criteria of what they called a muslim