--===== Create and populate a test table with the data given in the post.
     -- This is NOT a part of the solution
 CREATE TABLE #YourTable
        (
        SomeString VARCHAR(20)
        )
 INSERT INTO #YourTable
 SELECT '1230-544' UNION ALL
 SELECT '15C5487'  UNION ALL
 SELECT '132DE78'

--===== This solves the problem.
;WITH
cteSplit AS
(--==== This not only splits out the individual characters, it only splits 
     -- out the digits from 0 to 9
 SELECT SomeString,
        ROW_NUMBER() OVER (ORDER BY yt.SomeString) AS CharacterNumber,
        SUBSTRING(yt.SomeString,t.N,1) AS Character
   FROM #YourTable yt
  CROSS JOIN dbo.Tally t
  WHERE t.N <= LEN(yt.SomeString)
    AND SUBSTRING(yt.SomeString,t.N,1) LIKE '[0-9]'
)--==== This put's it all back together using a very high speed XML method
 SELECT t1.SomeString, 
        CAST((SELECT '' + t2.Character 
                FROM cteSplit t2 
               WHERE t1.SomeString = t2.SomeString 
               ORDER BY t2.CharacterNumber 
                 FOR XML PATH(''))
         AS BIGINT) AS NumbersOnly
   FROM cteSplit t1
  GROUP BY t1.SomeString