If you put two sticks of 16Gb 3200Mhz into your system then you will have 32Gb of 3200Mhz of RAM in your computer. Adding more sticks of RAM into your computer will not increase the speed, only the capacity.
You will have the same speed, but 3200Mhz is very fast and you do not need anything faster than that.
Make sure that when you buy more RAM that it is from the same company, preferably the same model. It might not work if they are from different companies (ex Corsair 16Gb & Team Dark 16Gb).
I hope I answered youre question, good luck.