When I was teaching customers at BAe flying college, Prestwick in the 1990s, the modular CPL syllabus (JAR) on a PA28 was 15 hours plus the test. Those who had been well taught during the PPL & IMC(IRR) rating had no difficulty achieving within syllabus hours. You had a fairly good idea as to how someone would shape up after the first exercise GH. Can they TRIM for S/L, climbing & descending? Answer YES ~ then comparative plain sailing. Most had been well taught by their flying clubs.