You may want to check if Cockpit fit copy parts. Only use genuine original parts for brakes. Copy parts can cause a variety of problems, such as scoring the discs if they are too abrasive (sintered pads), or lacking in stopping power. Conversely, overheating can occur if the pad is too soft.
In answer to your original question, 2.5 ml is coming towards end of pad life. At zero ml the pad will cut into and ruin the disc (expensive). You will know it from the horrendous squeal it makes.