You know of course that #2 is correct only if you are an employee. The employer must match that so the payment is closer to 15%. If you are self employed the cost is closer to 15%. Government program at its best. Paid quarterly. They don't want you to die before you have paid your unfair share.
The 7.5% is not paid by the employer because that is money that would have been paid directly to the employee if it wasn't mandated by the government. Mike