"but that's where you enter it using the ProSeries software."

That's not where to see it, though. This was asked:

"Also, can you use Medicare premiums for self-employed health ins and add a supplemental ins as well to box 15 sch C?"

I assumed that is supposed to be Line 15, not box 15. This is what the IRS tells you about Line 15

"15 Insurance (other than health)"

and here:

https://www.irs.gov/instructions/i1040sc

"Do not include on line 14 any contributions you made on your behalf as a self-employed person to an accident and health plan. However, you may be able to deduct on Schedule 1 (Form 1040), line 17, the amount you paid for health insurance on behalf of yourself, your spouse, and dependents, even if you do not itemize your deductions. See the instructions for line 17, Schedule 1, contained within the Instructions for Form 1040."