Are you sure? Remember that in addition to lowering the rate, it eliminates deductions and credits. So that 15% would be applied to your gross income, not to your adjusted income. You wouldn't be able to deduct your mortgage interest, medical expenses, charitable giving, etc. For someone taking the standard deduction, it might lower their taxes. But for anyone that owns a home, probably not.
Yes, my taxes would go down about $3,600.