I've been vaping 24mg juices from day one. Now I'm almost at the one year mark. The only time I use 20 or 18mg juice is in a more efficient delivery device (like a Kayfun), the 24mg juice is just too strong.
If I was still using Evods or Vivi Novas exclusively, I would still just be on the 24mg juice.
If you do want to cut down though, do it gradually. Just keep some of the higher nic juice around for stressful times. Or alternate between strengths so you don't get massive nicotine cravings.
A friend of mine at work cut out nicotine over a two year period, going from 24 to 18 to 12 to 6 then zero. He said the hardest step was the final one.