1. Many corporations pay less than 15% now, so you wouldn’t really be lowering their tax; you’d be raising it.
2. It would not bring in enough money. The national debt would increase and millions of government employees would lose their jobs.
3. The poor would not be able to afford to pay a 15% consumption tax and pay for food, housing, etc., so they would have to go on food stamps, welfare, etc., which would cost the government more than they were paying in taxes.
4. Most critically, the 15% import tax would violate international agreements, and force every other country in the world to prohibit imports of anything made in the U.S. This would mean, first, that U.S. exports would drop to zero, and, second, that only things that are used only in the U.S. could be made in the U.S.; anything used in more than one country could no longer be made in the U.S. (because what was used in the other country could not be made in the U.S., and it’s not cost-effective to make the thing in two different countries).
In conclusion, it wouldn’t really matter that you eliminated the income tax, because almost nobody would have an income. Nearly all jobs depend, directly or indirectly, on either (a) the existence of an income tax, so that the government can spend in ways that create jobs, or (b) the export of U.S. products to countries that won’t all imports from a country with a 15% import tax.