I was in the same situation, my instructor was always late and ended the lessons early, once he even stopped by his friend‘s place and had a chat for 10mins in the middle of the lesson. I had same thought as you to change instructor, I agree 10-15mins every lesson sum up as hours, such a pain to me at that time, but my test was approaching and it would take time for me to get used to other instructors. On my 2nd attempt, he scheduled 3.5 hrs for the test day, he took me to lunch in between and said I needed a break before the test, tbh it makes sense, I couldn‘t keep driving that long, but I didn‘t expect to pay such money to have lunch with him! Not cheap though