At the end of the day, you can only work with what you have at your disposal and make the best out of it. Being "slow witted" is only on the assumption that someone is faster witted than you but I think differently.
I think your thinking speed is yours and only yours. It's neither slow, nor fast, it is yours and nothing else matters. Especially not what people think, fuck people
In reality, everything we are, including our weaknesses, all work together to create the individuals that we are today. Embracing this weakness, like you've done and turning it into a strength is the only way to go.