Since there were no more comments to this question and no solutions were provided. I've looked into this with both university and work colleagues and we came up with the following solution:
SELECT TOP 1
T.ENTITY_NAME AS X
,T.SP_Y AS Y
dbo.TABLE AS T
T.SP_Y = @p_Y
AND T.SP_EAT_ID in (15, 16)
This was the chosen one due to be easier to read and achieving a similar performance to the first select.
For more details on the comparison. Please read the comment of "NeverJustHere" at 19-Feb-14.