When I am trying to make any turn (wide turns, change lanes, etc), the steering wheel becomes rough so i have to use 2 hands. However, this only happens when I'm driving the car slow like from 0mph to 15mph. Once the car starts moving at a faster pace or higher speed, the power steering works as intended. I have a 1990 rx7 gxl.

What is causing this issue and how do I fix it?

 

based on your other thread, I'd pop the hood and check the power steering belt tension.

 

I found out the power steering just needed some fluid. Probably a leak as well, but at least I know now.