The SS tax is 12.4%. When did that happen? When I used to have self-employment income I think I was paying at least 15%. You mean they have actually lowered the rate??
There is SS tax, 6.2% each from employer and employee (temporarily down to 4.2 for employees, I think). Then there is Medicare tax, something like 1.45%. Add it all together and you are correct, it’s > 15% for a self employed person, who pays the employer and employee share.
Minus the little deduction they give ya! Big of them.