I have absolutely nothing against the tempo in this fugue. I have heard it even slower and even as Olaf says, the D major is a festival key (only outranged by G major atmv), I think this tempo is perfect and perhaps late night at the festival?
What bugs me a bit is the prelude where you have problems. To be able to make these patterns even, you must provide each finger the same attention and time to produce a good tone. I would advice you to consult your teacher as it is difficult to guess your problem without seeing what you are doing. A daily slow practise in half speed or even slower might solve the problem but not for sure.
But if I make a guess. It sounds like the weak tones are produce by 4:th finger caused by irregular use of the thumb (most common problem). When you play a slow legato scale, how do you apply your thumb? Play a scale very slow (one key per beat in b=60 or similar), for instance RH ascending in C major. Once your thumb has released its key and finger 2 is pressing the D, the thumb should go under the palm to prepar to hit the F in time with correct strength, same thing for next time finger 2 is used. I think of this as finger 2 triggers the movement of the thumb. It might be hard to syncronise a continues movement (which comes automatically in fast speed) of the thumb. It sounds like your thumb is coming into action too late when you speed things up.
In this discussion, we might also end up in the confused thumb under/thumb over topic