This is not a gray area. When the improvements are complete, this is the date the improvements would be considered "placed in service" or "placed in use". Assets begin depreciation options and deductions on the date placed in service.
For example, if new appliances were installed depreciation begins on the date they can first be used. On the other hand if you are doing renovations such as a new roof, the roof depreciation begins when it is complete.
Since the actual work will not begin or be completed until 2017, the depreciation will begin in 2017.