dba_free_space is take too io

Hello

I have oracle 11.2.0.4 on oracle linux oparating system. following query working on db but it takes %70 io and when restart db again working. this should be less io and quick copmplete. are there any idea =

/* Formatted on 14.10.2018 12:32:34 (QP5 v5.294) */

  SELECT df.tablespace_name                                "tablespace",

         ROUND (df.bytes / (1024 * 1024))                  "size",

         NVL (ROUND (SUM (fs.bytes) / (1024 * 1024)), 0)   "free",

         NVL (ROUND (SUM (fs.bytes) * 100 / df.bytes, 2), 0)"%free",

         ROUND ( (df.bytes - NVL (SUM (fs.bytes), 0)) * 100 / df.bytes, 2)

            "%used"

    FROM dba_free_space fs,

         (  SELECT tablespace_name, SUM (bytes) bytes

              FROM dba_data_files

          GROUP BY tablespace_name) df

   WHERE fs.tablespace_name(+) = df.tablespace_name