AFAIK no one has made the fighters go slower.
However, if you don't like them always pinwheeling around the gravity well, then you can set them to hold position stance, and NEVER TELL THEM TO ATTACK AN ENEMY. Instead, move them up close to an enemy.
Why? They will automatically attack the enemy, but the will simply sit in the air, NOT MOVING. This has several benefits- better focusing of firepower onto enemy targets (only you can't really tell it what targets to focus on), and taking less damage from flak frigs.
The downside is that it is very micromanagement intensive, and you have no control over what units are attacked. It is quite effective though.