My income is lower in 2016 and with deductions I am in the 15% tax rate. Can I convert part of a Rollover IRA into a Roth IRA before April 15 to be taxed at 15% in 2016?

I noticed that my taxable income is significantly below the cut-off for the 25% tax rate. I would like to convert part of a Rollover IRA to a Roth IRA so that I can have that contribution only taxed at 15% — I think in the long term this is to my advantage. I discovered this in Feb 2017; is it too late to convert the money — i.e. did this need to be done before Dec 31 2016 or can I do this before April 15, 2017?