There is a common misconception that Windows uses some fixed amount of RAM at bootup and applications are then left to fight over what remains. This is not correct. Not even close.
Windows memory manager is always in control of RAM usage, the goal always to maximize performance, not minimize usage. At bootup system processes will be consuming considerable memory but that is only because there is currently no better use for it. When applications are run the memory manager will redistribute memory usage as necessary. I have seen this happen many times.
I see no cause for concern.