When you're going down the big slide wait for your health to regenerate and jump into the wall behind the slide and you should go down faster, i have not gone down using that technique yet. Hope this helped

P.S: Treyarch do need to fix it

-AWP

I have tried this I find if you stay as far left as possible going down the last part and just drop off instead of jumping it works the best .. if you aim for the bottom of the first slide before AN-94 room I find you have the maximum success thanks for the tips though much appreciated