There are many reasons a system may use a bit more or less RAM at idle, depending on how you installed it and what software you have installed as well as other customizations you have.
On Zorin OS Lite, I use conky with several HUD's for system monitoring that startup within a few seconds of loading the desktop. Terminal window also opens.
Yet, at idle, it will generally sit at under 1% usage or under 700 megs.
On my build of Zorin with Cinnamon, the average was 3% at idle or 1.4 gigs and on Linux Mint, slightly higher at 4-5% or under 2gigs.
Other users may have different setups and not use conky. They may see different results. But using 956megabytes at idle is not bad in modern computing, not at all... Hardware just keeps demanding more and at idle, many new computers will consume a lot as the drivers keep pace with the latest hardware.
Measuring at idle is a lot like measuring the quality of a race car when it is sitting on the track motionless with the engine idling.
Pointless.
Also RAM does not dump all stored memory immediately. It is kept in case it is needed again, so only when RAM is being used with intensity does RAM start dumping to clear space. How long the idle computer sits factors in - since RAM will accrue more filled space the longer it sits, even if you booted up the computer, then went and drank coffee for three hours and never launched a single program or instance during that time.
I can easily set up a machine that uses well under 400 megs on any Desktop Environment, be it Gnome, XFCE, LXDE, Cinnamon... just by turning a bunch of stuff off and disabling certain Hardware functions.
But, once I decide to start the race, I will be driving in a 1974 Fiat 500 while everyone else is in Ferrari's. If I can hit 60mph at all, it will take a couple of minutes to get there.
Performance during usage is the metric by which we gauge uhh.... performance.