Is that all that's on your tax returns? Under whose name is the mortgage? And who made the donations?
You're not by any chance claiming the full mortgage interest on both your and your wife's return when doing in MFS are you?
Assuming that there's nothing else on your tax returns, I can see how this would happen. Your itemized deductions add up to $22,200. The standard deduction for MFJ is $12,600, and your two exemptions are $8100 total. This means your itemization of deductions only decreases your taxable income over using the standard deduction by $1500 under MFJ. Your combined taxable income is 183,400-22200-4050*2 = 153,100, which results in $29611.58 of tax liability.
Using MFS, assuming all of the charitable giving and mortgage interest paid was done by you, your itemized deductions would total $22,200, decreasing your taxable income over using hte standard deduction by $15,900. Your taxable income would become $80750, resulting in a tax bill of $16102.75.
Your wife takes the standard deduction. Assuming all the interest was in her name, her taxable income would be $66,050, resulting in a tax liability of $12283.75.
So under MFJ, we have 29611.58. Under MFS, we have a total of 28386.5 The savings under MFS under my assumptions is $1225.08. I made assumptions that would maximize the difference.
EDIT: tl;dr: Generally speaking itemized deductions are one area where people experience the marriage penalty. If you're filing single, your itemized deductions only need to overcome the standard deduction $6300 (for 2016) for itemization to benefit you. But if you're filing MFJ, your total itemized deductions need to overcome the MFJ standard deduction $12,600. Furthermore, it's only the amount by which your itemized deductions exceed the standard deduction. If one person has most of the itemized deductions in their name and the other doesn't, then taxes will be higher filing MFJ.
P.S: Make sure filing MFS doesn't exclude you from these deductions. I know MFS excludes you from a lot of things.