Complex sentence: A modern communication tool is only compatible with Sign Language when it has at least 15 frames per second (fps) and a minimum resolution of 320 x 240 pixels, so the tool is fast and large enough to capture Sign Language movements.
Split into simpler sentences: A modern communication tool is only then compatible for Sign Language when it has at least 15fps and a minimum resolution of 320x240 pixels. So that it is fast and large enough to capture Sign Language movements.