Your presets folders can get very bloated if you add too much to them - deleting the icon doesn't delete the object in the folder. I got a very good tip here on the forum about a week ago........When you're starting a new project like this, create a new Temporary Folder in your presets (or several, one for objects, one for materials etc.) and save what you want into that, or import freebies that you want to use just once. Then when you've finished your render you can delete the temporary folders if you want to.