It's also important to know if you are in a community property state or not.
Also, your depreciation is probably wrong from square one. Land never depreciates, you only depreciate the cost of the buildings and other things attached to the land. If this "condo" includes shared ownership of land, common areas, and so on, that should have been accounted for.
I believe, that if you truly had no ownership interest, and you fully inherited the property in 2015, then you received a stepped up basis equal to the FMV on the date of the previous owner's death. You should have reset the depreciation to year one at the 2015 FMV (minus the FMV of the land). I also believe you were the inheritor as of 2015, even though the paperwork didn't clear until 2020. However, if the estate reported the rental income on form 1041 (the estate tax return), then your basis might only reset when you were awarded the deed in 2020. It really is a situation that requires an attorney and an accountant.
If your spouse calculated the depreciation wrong starting in 2005, and you filed joint returns, you are jointly liable for that misstatement. However, the statute of limitations has run out for most past years.
You're asking about capital gains so did you sell? You are correct, your basis reset to FMV in either 2015 or 2020 and you should have reset the depreciation to the new basis and started a new 27.5 year clock. The capital gains and depreciation recapture if you sold or are planning to sell is based on the depreciation you should have claimed, not the depreciation you actually claimed. To correct prior incorrect depreciation, you will file form 3115 rather than filing amended returns. You will also need an accountant to prepare form 3115 for you, it's not a layperson level form and it is not supported by Turbotax.
