I cannot provide one single source; I'd have to provide dozens.
Yes. Because there is no source. You are making your own subjective assumptions that relate only to selectively pruned highlights and presenting them as if scientific truth. You are not arguing for anything that a single scientific paper directly suggests as the best approach.
I guarantee that my advice will work. For it not to work will go against everything we have learned about the brain, especially in the past decade.
Don't be so bloody naive! Simply repeating something over and over does not magically provide a deep memory. It's exactly what provides the shallow and superficial physical memory that most of us suffer from- UNLESS you are finding a whole wealth of different approaches to how you think about what you are doing in that time. If it were as simple as throwing loads of time at 4 bar groups, as you suggest, almost nobody would have memory problems.
Man up and attribute your speculative interpretations of selectively chosen scientific tit-bits to yourself. People like yourself give science a bad name- by making wild speculations of their own and claiming that science itself is responsible for them. Do you seriously think that it takes 15 minutes- regardless of the difficulty or complexity of a passage? And this will cause anything to be solidly memorised by default? It's plain foolish to attribute an exact time scale, without consideration of both specific factors to the music and the specific abilities of the person attempting to memorise it. It's also very naive not to consider the QUALITY of what is being done- rather than merely a timescale. You may be capable of memorising isolated snippets of published scientific papers, but you show no ability to think like a scientist when it comes to extrapolating from those points in a logical and self-critical manner.
BTW, you didn't even answer the OPs question; you just criticized mine. Your advice is to not even attempt to try what I suggest because it contradicts your opinion.
Obviously you didn't read my reply carefully. What I said was that your advice merely scratches the surface- not that I disagree, exactly. It's simply that repetition alone is worthless- unless you do it with the right qualities and thoughts. By omitting these issues from your advice, you omit virtually everything of genuine importance. That's why I pointed out the value of the one finger practise method- which is worth 100 thoughtless repetitions of a passage. To improve memory, a person needs to engage more ways of thinking and processing the musical construction. Merely repeating things leaves you stuck in your typical ways of thinking- inspiring minimal improvement, unless you force yourself into alternatives. When the only plan is to repeat something for 15 minutes (rather than to find a wealth of different viewpoints during those 15 minutes) there might as well be no plan at all.