As Critter said, the $25,000 allowance means it can be used in the current year. If the Passive Losses are not allowed, then it is carried forward.
If claiming the rental losses create a Net Operating Loss (Line 41 of your Form 1040 will be negative), then you can either make an election to carry it forward, or you can amend your 2014 return to claim the Net Operating Loss (type "NOL Carryforward" in the search box in the program). If TurboTax doesn't calculate the amount of the Net Operating Loss, you will need to calculate it manually.
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