The rule is easy - the more pieces you learn the faster you learn the next ones. When you try to learn piece above your level you need more time than to learn piece at your level. (Of course to improve you have to learn pieces from the level above.) The same is with pieces from ACTL level, if it's your level it's a normal thing to learn this kind of pieces in a few months. There are people who are above it and can learn these pieces in days...
"Can someone give me an advice on how to play the fast part faster."-Start whith everything of Czerny, Clementi and Scarlatti, all Mozart and Beethoven sonatas, Brahms exercises and Bach WTC book 1 and book 2, almost everything of Schumann and Schubert. After that, Chopin nocturnes and then some of the etudes.
I do hope you got a money back refund on that lobotomy.Everything by Clementi and Czerny and FI would be sightreadable.(My spellcheck recognises Czerny, but not Clementi - Apparently technology is no match for philistinism)