Remember, you dosed 2ppm yesterday right? so that converted to nitrIte. Since you reading stayed the same, but the ammonia is gone, you converted 1.5ppm nitrIte to nitrAte.
Keep an eye on things, this is where I got stuck. I stayed doing this for a week. I skipped a day dosing to finish up. Since I was converting 1.5-2ppm a day, when I didn't feed ammonia, I was able to take out the remaining nitrIte, and then continue to convert 2ppm ammonia, now all the way through nitrAte, in 24 hours.
Just a thought.