Data manipulation in SQL
Use following WHERE predicate 

-- data (Jan-Dec) of the year 2015
year = 2015  OR
-- data for the year 2014 from May-Dec
year = 2014 and month in ('May','Jun','Jul','Aug','Sep','Oct','Nov','Dec')


Adjust the column names and/or litaral values as required.
If the month is stored as number you may use month between 5 and 12