Pandas dataframe to set all columns to be character length fixed

I have a csv file which column names are fixed width of 15. And its elements length different, depends on the data type.

Original

Name           ,Date           ,Time           ,TST Num        ,Dept/Dest      ,Tst Level      ,AAS            
AAAAAA         ,18/12/2007     ,07:57:40,AAA101         ,AAAABBBB       ,220,320
BBBBBB         ,18/12/2007     ,12:34:06,AAA112         ,XXXXYYYY       ,210,320

I will use Pandas to work on it. And the final output should look like:

Final

Name           ,Date           ,Time           ,TST Num        ,Dept/Dest      ,Tst Level      ,AAS            
AAAAAA         ,18/12/2007     ,07:57:40       ,AAA101         ,AAAABBBB       ,220            ,320
BBBBBB         ,18/12/2007     ,12:34:06       ,AAA112         ,XXXXYYYY       ,210            ,320

I can convert each column like:

df = df.astype(str)
df['Time           '] = df['Time           '].apply('{:15s}'.format)

But I can’t do in this way:

all_columns = list(df)
df[all_columns] = df[all_columns].apply('{:15s}'.format)

Is there any way I can do it without a loop?