It is quite difficult to achieve that speed. My teach and I did do them a little slower, but gradually I brought them up to full speed. My advice, practice them SLOWLY a lot, challenge yourself by dropping certain notes but keep the rhythm, so if you skip two sixteenth notes, then wait an eighth note and continue, see what i mean? Speeding through these with lots of mistakes TOTALLY ruins the point of these exercises. They are meant to teach you speed and dexterity, so playing them perfectly and just slightly under tempo is better. If you are unable to come close to full speed, do Czerny Op 740 "Art of finger dexterity" they are slower and not as hard, and in my opinion are better than Op 299.