Slicing a python dataframe from a string date column

Question

I am trying to slice a dataframe based on their str date values. I only want to keep records of the last 15 days.

When I try this

df_master_recent_date= df_master['Datetime_col'] > (datetime.now() - pd.to_timedelta("15day"))
     

I get error : TypeError: '>' not supported between instances of 'str' and 'datetime.datetime'

When I convert the df_master['Datetime_col'] to date

df_master_recent_date = datetime.strptime(df_master['Datetime_col'],'%Y%M%D') > (datetime.now() - pd.to_timedelta("15day"))

I get error TypeError: strptime() argument 1 must be str, not Series

At the beginning of the code I convert the entire dataframe to str with this df_master= df_master.astype(str)

Date format in the column is '21/02/2022 12:21:00'

I understand the errors, and the second error likely to be resolved with a for loop which I need to figure how to construct, however, does anyone knows how to get this working without a for loop, or with the for loop if one line is not possible. Thank you.