It certainly seems so. My plan renews on the 2nd, right now I have 3% left. Ever since I reached the 10% and my meter turned yellow, things have been ridiculously slow. As in loads simply timing out, me staring at white boxes where images should be (that never load or only load much, much later).
I get that data speeds are throttled AFTER the regular data is used up, but why is this happening before I run out?
Why it's slower at this point could be due to a lot of things, but the fact that it coincided with dropping below 10% remaining data is a coincidence. Your speed is not deliberately throttled at any other time than when in FAP, and that only happens when you are out of data.