Bounty Hunter 15 (Source)

Droid speed is used to decrease the time taken for the droid to report back using the "find" feature of the droid.

Droid Tracking speed is used to decrease the time taken to report back using the "track" feature.

Since i'm here, i'll explain what the other droid related mods do.

Droid Precision decreases the chance of the droid being eaten by a mynock or being destroyed by a meteor when trying to find which planet the mark is on.

Droid Tracking effectiveness decreases the chance of the droid loosing the mark when using the "track" feature.

Tracking Droids adds to how many more times the droid can report back on the location of the mark, all depending on the Droid Tracking effectiveness of course.

IE. You might have alot of Tracking but the effectiveness is low, so it might only report back 3 times out of a possible 10 due to a low effectiveness.