drag on vs prolong

drag on

verb
  • to last too long 

prolong

verb
  • To become longer; lengthen. 

  • To lengthen in time; to extend the duration of 

  • To put off to a distant time; to postpone. 

  • To extend in space or length. 

How often have the words drag on and prolong occurred in a corpus of books? (source: Google Ngram Viewer )