I wouldn't be so sure about that. This is actually a huge misconception most people have; that adding RAM will speed up a computer. More RAM is only really beneficial if the system runs out of RAM. And still, the system can only perform as fast as the CPU. Adding more sticks can actually cause the RAM to slow down on some motherboards.
So will it improve performance in your case? Maybe yes, maybe no... The less the system uses a swap file, the faster performance will be. However, if you have very little running in the background and a swap file isn't being used, it shouldn't help much at all.