"They claim I miscalculated my taxes on Line 15." The IRS will use this terminology whether or not you made the calculation or a tax professional did or some software did.
If there is a difference on line 10, then of course there may be a difference on line 15. These Notices are sometimes hard to follow, but you want to find the first discrepancy between your entries and the IRS' corrections and then concentrate on that.
If after reviewing the letter and your return, you still don't understand the discrepancy, then please go visit the TurboTax Audit Support Center, and check out the helpful advice there.
Alternatively, you may respond to the IRS by telephone or mail. Please see "Understanding your CP11 Notice" at the IRS for more information.
