Offset date for a Pandas DataFrame date index

Marginally shorter/more direct is tshift:

df = df.tshift(15, freq='D')

Link to a list of freq aliases

you can use DateOffset:

>>> df = pd.DataFrame(np.random.randn(6),index=dates,columns=list('A'))
>>> df.index = df.index + pd.DateOffset(days=15)
>>> df
                   A
2013-01-16  0.015282
2013-01-17  1.214255
2013-01-18  1.023534
2013-01-19  1.355001
2013-01-20  1.289749
2013-01-21  1.484291