iris pro graphics 1536 allocated memory is always full on my macbook 15 2015

I am having a problem with my second-hand MacBook pro 15 2015, I got it second hand and already updated to big sur 11.0. the problem I have is jankiness in web scrolling and a lot of times, I get lags when typing (happened when typing this post). this actually stops being an issue when I close certain apps like phpStorm IDE, chrome tabs, … . I traced the issue to the allocated VRAM being quickly filled by the apps I am running. I find it weird that I have 16GB of ram that is still not completely used while my 3GB swap partition is nearly filled.

I personally never had such issues even on 8GB ram ( I now have a 16GB model). i had hackintoshes before and there was never an issue with jankiness when opening many apps and using up to 13GB of RAM at times.
my current machine is running at 1920×1080 resolution 16:10 and HiDPI (probably the culprit). It has an Iris Pro graphics 1536 MB, R9 AMD DGPU, and i7 2.8Ghz.

my goal is to get rid of this memory issue while trying to keep the HiDPI mode on the screen (i am using screenResolutionX to get the resolution).