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Texture filtering can be controlled via the Renderer Appearance sidebar: https://dl.dropboxusercontent.com/u/119 ... tering.jpg
To open the sidebar, type "rendedit" in the console or go to Config > Renderer and select "Edit" in the Appearance dropdown menu.
You should set Texture Filtering to "None", and uncheck the Bilinear checkboxes.
This screenshot is from the latest 2.0 build, but 1.15 should work mostly the same.