I am not sure about significant, but yes you get a savings on tax due on the rental income profit.
If you have never depreciated the property you will add it as an asset. You should use the date originally put into service six and one half years ago. The basis is the amount paid for the property plus improvements. If you lived in the property before placing it into service you would use the purchase price or fair market value which ever is less.
You would depreciate over 27.5 years. TT will calculate any depreciation for prior years. If any depreciation over the prior three years was significant enough to change your tax return...you may amend the prior three years for a refund. The IRS only allows 3 years to claw back refunds.
Best of luck to you!