Problem with a conditional probability

hi. I'm trying to face a problem with the conditional probability. I have to simulate this probability

My idea was to find the values of API between the two values and for these values i search the corresponding values of SSM. At the end i make a simple probability on the SSM values that i take previously and sk values.

For the first part for finding API values and corresponding SSM values i write this script, but is too slow on running.

There is a more easy way for writing it? Thank you all