Based on the comments I am going to try to answer own question but should still be grateful for any additional input. (The sentence came from 総まとめ N2 読解 p110 if anybody is interested.)
In the case of Shoji, if one part is torn you would never replace the whole thing. In fact, in the first instance you would not even replace the paper of the torn 15cm square panel. First you restore the damaged area by pasting something like a coloured piece of paper in the shape of an autumn leaf over the torn hole....
1. The sentence has the structure S1ばかりかS2 where S1 and s2 are both
In the case of C, you would never do A. Not only that but you would not even do B in the earlier stages (of C)
- B being a lesser activity/action than A.
- Also note that when S1&S2 are both negative ばかりか can be replaced by どころか.
2. Some understanding of context and maintenance of Shoji helps:
The sentence comes from an essay on how it is easier to replace modern machines in the entirety when one part breaks down. The writer draws a contrast with the maintenance of Shoji, which often come with panels (or panes?). A small tear is patched over with a pretty piece of paper, which from the writer's perspective, makes the Shoji even prettier. Eventually as the number of tears grows and the Shoji gets shabbier a whole sheet or perhaps event the Shoji would be replaced. (See links in Chocolate's comments for more background)
I think (!) 枡の１５センチ角 refers to a 15 cm square pane on the shoji. (枡 being used for the square boxes in which sake is served or the box seats around the Sumo dojo. 角 is square)
References: (1) Dict of Intermed. Jse Grammar p11, (2) Comments above