Cần giúp đỡ tối ưu SQL Query giảm thời gian truy vấn

 SELECT 
 		A.SlpName
 		,A.[Year]
 			,A.Region
 			,A.RegionName
 			,A.CardCode
 			,A.CardName
 			,A.[Type]
 			,SUM(A.AmtBefDi) AS AmtBefDi	
 	FROM
 	(
 		--New
 		SELECT 
 				T1.SlpName
 				,T.[Year]
 				,T.Region
 				,dbo.fn_GetRegionName(T.Region) AS RegionName
 				,T.CardCode
 				,T.CardName
 				,'New' AS [Type]
 				, SUM(T.AmtBefDi) AS AmtBefDi
 		FROM dbo.DTS_SUMMARY_SALES_AR AS T
 		LEFT JOIN DB_SAP.dbo.OSLP AS T1 ON T1.SlpCode = T.SlpCode
 		WHERE T1.Locked != 'Y'
 		AND T.Legal = @Legal
 		AND NOT EXISTS( SELECT T1.CardCode 
 						FROM dbo.DTS_SUMMARY_SALES_AR AS T1 
 						WHERE T.CardCode = T1.CardCode 
 						AND T1.[Year] < T.[Year] - 1 
 						AND T1.Legal = @Legal
 						GROUP BY T1.CardCode 
 						HAVING COUNT(T1.CardCode) > 0)
 		GROUP BY T.SlpCode
 				,T1.SlpName
 				,T.[Year]
 				,T.Region
 				,T.CardCode
 				,T.CardName
 		UNION ALL
 		--Loss
 		SELECT 
 				T1.SlpName
 				,T.[Year] + 1 AS [Year]
 				,T.Region
 				,dbo.fn_GetRegionName(T.Region) AS RegionName
 				,T.CardCode
 				,T.CardName
 				,'Loss' AS [Type]
				, SUM(T.AmtBefDi) AS AmtBefDi
 		FROM dbo.DTS_SUMMARY_SALES_AR AS T
 		LEFT JOIN DB_SAP.dbo.OSLP AS T1 ON T1.SlpCode = T.SlpCode
 		WHERE T1.Locked != 'Y'
 		AND T.Legal = @Legal
 		AND T.[Year] < @Year
 		AND NOT EXISTS( SELECT  T1.CardCode 
 						FROM dbo.DTS_SUMMARY_SALES_AR AS T1 
 						WHERE T.CardCode = T1.CardCode 
 						AND T1.[Year] = @Year
 						AND T1.Legal = @Legal
						GROUP BY T1.CardCode HAVING COUNT(T1.CardCode) > 0) 
 		GROUP BY T.SlpCode
 				,T1.SlpName
 				,T.[Year]
 				,T.Region
 				,T.CardCode
 				,T.CardName
 		UNION ALL
 		--Remain
 		SELECT 
 				T2.SlpName
 				,T.[Year]
 				,T.Region
 				,dbo.fn_GetRegionName(T.Region) AS RegionName
 				,T.CardCode
 				,T.CardName
 				,'Remain' AS [Type]
 				, SUM(T.AmtBefDi) AS AmtBefDi
 		FROM dbo.DTS_SUMMARY_SALES_AR AS T
 		INNER JOIN ( SELECT T1.CardCode  , T1.SlpCode
					 FROM dbo.DTS_SUMMARY_SALES_AR AS T1 
 					 WHERE T1.[Year] < @Year AND T1.Legal = @Legal
 					 GROUP BY T1.CardCode , T1.SlpCode
 					 HAVING COUNT(T1.CardCode) > 0) T1 ON T1.CardCode = T.CardCode AND T1.SlpCode = T.SlpCode
 		LEFT JOIN DB_SAP.dbo.OSLP AS T2 ON T2.SlpCode = T.SlpCode
 		WHERE T2.Locked != 'Y'
 		AND T.Legal = @Legal
 		GROUP BY
 				T.SlpCode
 				,T2.SlpName
 				,T.[Year]
 				,T.Region
 				,T.CardCode
 				,T.CardName
 		UNION ALL
		--Back
		SELECT
 				T2.SlpName
 				,T.[Year]
 				,T.Region
 				,dbo.fn_GetRegionName(T.Region) AS RegionName
 				,T.CardCode
 				,T.CardName
 				,'Back' AS [Type]
 				, SUM(T.AmtBefDi) AS AmtBefDi
 		FROM dbo.DTS_SUMMARY_SALES_AR AS T
 		INNER JOIN (	SELECT 
 								T1.CardCode
 						FROM dbo.DTS_SUMMARY_SALES_AR AS T1
 						WHERE  T1.Legal = @Legal
 						AND T1.[Year] < @Year - 1
 						GROUP BY 
 								T1.CardCode
 						HAVING COUNT(T1.CardCode) > 0) T3 ON T3.CardCode = T.CardCode 
 		LEFT JOIN DB_SAP.dbo.OSLP AS T2 ON T2.SlpCode = T.SlpCode
 		WHERE T2.Locked != 'Y'
 		AND T.Legal = @Legal
 		GROUP BY T.SlpCode
 				,T2.SlpName
 				,T.[Year]
 				,T.Region
 				,T.CardCode
 				,T.CardName
 	) A
 GROUP BY 
 		A.SlpName
 		,A.[Year]
 		,A.Region
 		,A.RegionName
 		,A.CardCode
 		,A.CardName
 		,A.[Type]

Em run thì nó chạy trừ khoảng 14- 17s . Không có biết có cách nào làm cho việc truy vấn nhanh ko ?
Store Procedure này em dùng để query ra những khách hàng mới, mất , trung thành, trở lại từ quá khứ đến hiện tại ?