Note that line 15 on Schedule C is labeled (on the form) as "Insurance (other than health)".
Your self-employed health insurance deduction belongs on line 29 on page 1 of the 1040.
These are not the same thing. Schedule C line 15 is where you enter business insurance premiums, not health insurance. Form 1040 line 29 is where you enter health insurance premiums you paid for yourself, your spouse, and your dependents.
Note: Schedule C line 14 is where you include health insurance premiums you paid for your employees, if applicable.