I went to the eye doctor a few days ago they said my vision went down to in my right eye 15/20 while my left is 20/20 and she said its because of eye strain due to the computer and phone. how long will it take my eyes to go back to 20/20?

It is hard to say when, or even if, your eyesight will return to 20/20. But, when you are using your computer or phone, you should periodically look into the distance. This will help avoid eye strain and help to lessen nearsightedness, also called myopia. See your eye doctor at least yearly. If you notice increased blurriness, see your eye doctor sooner. Best of luck to you!