Junior Guildhall audition help!!!

[cjcarrington97]

As you can tell, I am in some, (quite a lot actually), need of help and advice on an audition for entering Junior Guildhall's department in London, (Guildhall School of Music and Drama). 

I am hoping to play in terms of two contrasting pieces:
 - Bach Prelude and Fugue No.6, BWV 875, D Minor
 - Beethoven Sonata No.16, 1st Movement, G Major

Any advice on whether these pieces are good for the audition as I don't know if I've thought hard enough about the contrast or complexity, however I'm aware that they are looking for potential, not finished talent.
By no means do I want to go to the concert stage professionally, but right now I just want to develop my skill and passion for the piano and be opened up to a more musical environment.
To mention - I am 15, (will be 16 when I do the audition), years old.
 I know this is late, but better late than never hey!

This is almost a gamble as I would never have considered such a prestigious place to study however after spending a day there, I felt completely comfortable and could definitely see myself going there, (and would put the work in!).

The only problem I suppose is that even though I have a piano tutor, he has never worked on getting students into music colleges, (just focussed on grades and diplomas by the worst board LCM!).
I have achieved grade 8 leisure play at distinction, and I'm due to take my DipLCM next year.
From this, I would be incredibly grateful for advice and help on being ready for the audition and actually having a chance in getting in.

I mentioned that I did grade 8 leisure play and so never studied scales as religiously as most, however I am familiar with most and can play them well with a little practice. The problem here is that me and my tutor are both in the dark about this requirement. They say you should give a list of 5/6 scales and arpeggios to recite at the audition which makes sense. The problem here is, (because it is grade 8 level), do the 1 major and 2 minors could as 3 scales altogether? In terms of arpeggios, if I supplied C major as one for instance, would i be expected to play root and 1st/2nd inversions as one of the arpeggios as well, or would they be separate?
I am probably overthinking on this, however I really don't understand how it works and neither does my piano tutor, so I want to be completely clear...
(Anyone that has auditioned and had to play scales - especially if you auditioned for Guildhall -please clear this up for me as I am really confused).

In terms of sight reading, even though I never did this in grades, I have to in my diploma and I am a fairly good sight reader (grade 7/8), so I think this will just require practice.

Lastly, I have to partake in a musical discussion, (or viva voce). If anyone who has taken an audition for music college could give me example questions of what they may ask relating to my two pieces, then I would be wholly appreciative. Being fair, my musical history and context of composers in general is quite good, (which is surprising because I've never had to do an exam on this before). I think the theoretical side will be a tad more difficult for me.
What's also useful is that in my diploma I have to partake in a discussion as well, so my tutor should be able to help with that.
I may also be asked about my musical endeavours which I think is the only part of the audition I'm not worrying about!

So to conclude, any advice and help/guidance on this process will be completely welcomed as I am in much need of it. -- I don't know if I'm over-thinking this, or I have my head stuck in the clouds.
All I do know is that I really want to get in.