@BIG-YOSHIKI It will be both System and GPU memory. Based on your specs, you should be in great shape.
But there are other factors such as the visual settings (in game), having updated video drivers, use of visual mods and ENBs that could adversely impact FPS/performance/texture loss. Even a HDD or SSD that is almost full can be part of the problem.
From my own experience, and others can chime in, I will experience texture loss from spawning way too many cars or peds or MLOs. The location on the map comes into play as well. Add a huge map or Forests of San Andreas and you will possibly get FPS drops followed by the texture loss.
You haven't been specific as to what mods you have installed, how your game is configured, what does "buggy textures" mean and if the issue is all over the map or in certain areas of the map.