Parallelizing creating list of lists using multiprocessor

Question

I am creating a list of lists using a function that takes a long time to calculate each of the list elements. Since this is slowing down my whole process, I'm trying to make it run faster by using the multiprocessing library in python.

However, When I try to use the multiprocessor, it makes my code run even slower. Any idea why this is happening?

import multiprocessing
import time

# arbitrary F function for a reproducible example
# The actual function is more complicated
def f(a, b):
    for i in range(100000):
        a = True
    return [a * b, a + b]


if __name__ == '__main__':
    G = [1, 2]
    l = [t for t in range(6000)]

    t1 = time.time()
    my_list1 = [[f(l[x], G[i])[0] for i in range(len(G))] for x in range(len(l))]
    t2 = time.time()
    print("Original: ", t2 - t1)

    pool = multiprocessing.Pool(processes=multiprocessing.cpu_count())
    t3 = time.time()
    my_list2 = [[pool.apply(f, args=(l[x], G[i]))[0] for i in range(len(G))] for x in range(len(l))]
    t4 = time.time()
    pool.close()
    print("Parallelized: ", t4 - t3)

example Output:

Original:  29.832287073135376
Parallelized:  33.75640296936035

Any notes on how I can create this list in parallel are appreciated.