DROP TABLE IF EXISTS #MyTable1;

CREATE TABLE #MyTable1 (Value real);

INSERT INTO #MyTable1 
	(Value)
VALUES
	(201.7445), (23.60291), (178.1416), (286376.8), (218775.3), 
        (67601.47), (10), (10.0), (10.00), (-1),
        (-1.2), (-1.02), (-201.7445), (0), (Null);;

SELECT
	Value
	,TRIM(STR(Value, 15,3)) AS [STR_15_3]
	,TRIM(STR(Value, 15,8)) AS [STR_15_8]
	,CAST(Value AS NVARCHAR(Max)) AS [NVARCHAR(Max)]
	,CAST(Value AS DECIMAL(15, 3)) AS [DECIMAL_15_3]
	,CAST(Value AS DECIMAL(15, 8)) AS [DECIMAL_15_8]
FROM
	#MyTable1;

DROP TABLE IF EXISTS #MyTable1;

CREATE TABLE #MyTable1 ( Value real);

INSERT INTO #MyTable1 
	(Value)
VALUES
	(201.7445), (23.60291), (178.1416), (286376.8), (218775.3),
	(67601.47), (10), (10.0), (10.00), (-1),
	(-1.2), (-1.02), (-201.7445), (0), (Null),
	(0.0001), (-0.0001), (0.0000000001), (-0.0000000001);

SELECT
	Value
	--,CONVERT_Value
	--,[CHARINDEX]
	--,CountOfLeftSymbols
	--,CountOfRightSymbols
	,CASE 
		WHEN CountOfLeftSymbols + CountOfRightSymbols <=15 THEN 
			CASE CountOfRightSymbols
				WHEN 0 THEN CAST(Value AS DECIMAL(15, 0))
				WHEN 1 THEN CAST(Value AS DECIMAL(15, 1)) 
				WHEN 2 THEN CAST(Value AS DECIMAL(15, 2)) 
				WHEN 3 THEN CAST(Value AS DECIMAL(15, 3)) 
				WHEN 4 THEN CAST(Value AS DECIMAL(15, 4)) 
				WHEN 5 THEN CAST(Value AS DECIMAL(15, 5))
				ELSE CAST(Value AS DECIMAL(15, 6))
			END
                --ELSE
		--	
	END AS [DECIMAL]
FROM
	(SELECT
		Value
		,CONVERT_Value
		,[CHARINDEX]
		,IIF(
			[CHARINDEX] > 0,
			LEN(LEFT(CONVERT_Value, [CHARINDEX]-1)),
			LEN(CONVERT_Value)
		) AS CountOfLeftSymbols
		,IIF(
			Value != 0 AND [CHARINDEX] > 0,
			LEN(RIGHT(CONVERT_Value, LEN(CONVERT_Value) - [CHARINDEX])),
			0
		) AS CountOfRightSymbols
	FROM
		(SELECT
			Value,
			CONVERT_Value,
			CHARINDEX('.', CONVERT_Value) AS [CHARINDEX]
		FROM
			(SELECT
				Value
				,REPLACE(CONVERT (VARCHAR(MAX), Value, 128), '-', '') AS CONVERT_Value
			FROM
				#MyTable1) t1) t2) t3;