The mean AO index figure for winter 2014/15 was +0.85. This is one of the highest figures in the historic series going back to 1950. So the OPI was a very poor predictor of the AO index this year.
Highest DJF AO index mean figures
1988/89 2.69
1992/93 1.77
1989/90 1.25
1999/00 1.13
1991/92 1.09
1972/73 1.09
2006/07 1.00
1975/76 0.99
2007/08 0.86
2014/15 0.85
So winter 2014/15 saw the 10th highest AO index in the last 65 years