RAM adds capacity, not performance. That means that the answer to your question depends entirely on whether you are already running low on RAM, and that additional capacity, if added, will be used.
Adding additional RAM will have a huge impact on a system that's already using most of its memory, but will have essentially no impact on a system that is only using half its existing capacity.
it sounds like in your case, that some more ram will help you when your system is under a non-negligible load, so it will reduce system slow-down as more load is introduced, until the new capacity is expended. It won't improve performance when the system is idle though.