My wife and I are self employed and own our business do we pay the 15.3 % self employment tax together or do we both have to pay 15.3% separately ?

I assume that you are filing jointly. Complete a Sch C for each of you. TurboTax will calculate the self employment tax on the income for each of you and combine it into one total. 

The 15.3% self-employment tax would be calculated separately and put on the 1040 return.  Spouses can elect to be treated as a qualified joint venture.  This election is made on the 1040 return by dividing all items of income, gain, loss, deductions, and credit between them in accordance with each spouse's interest in the business.  

Self-employment tax would be calculated by TurboTax for you based on your computation of the Schedule C form.  As @Bsch4477 stated, you will create a Schedule C for yourself and one for your wife.  The allocations made on the Schedule C form will be used to allocate the amount of Self-employment tax that is owed by each party.  

To create two Schedules C in TurboTax, follow these steps:

1. Click Wages & Income
2. Click Add/Edit on Self-Employment
3. Enter allocated items for yourself
4. Once back on the Self-Employment Screen, Click Add another line of work
5. Enter allocated items for your spouse.

Please see the following link for more information:

Qualified Joint Venture

@jgotti-9