I have no first-hand experience of the other schools you're looking at, but you won't go wrong with Bristol. However, we're all different - just because they worked for me, doesn't mean they will work for you. Visit all three, get a sample of their notes, and see which set of notes you think you will be able to study from the easiest. Also ask if it's possible to sit in on a half hour or so of their brush-up.
As for your other questions:
1) I managed it, working 5 days a week, but I didn't have a social life for a year. As for 15 hours per week... well, I guess technically 1 hour a week would be ok, except it would take a little longer! But yes, 15 hours sounds reasonable.
The problem, though, won't be passing the exams with 15 hours per week. The problem will be finding the motivation to put in 15 hours per week every week throughout the course. Once you get your notes, I would think in terms of the number of frames/chapters/whatever that you want to complete each week, and put in as many hours as you need to in order to achieve that.
2) Progress tests were always returned very promptly. I only needed extra help a couple of times while I did the course, but each time I e-mailed a question and got a reply from the appropriate instructor the next day. Can't fault them at all here.
3) How long is a piece of string? Took me 12 months exactly, but it will depend how quickly you work through the course!
FFF
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