You would need to copy your dom2.exe, rename the copy to dom214.exe (or anything really), and apply the patch. Only the original dom2.exe will be patched to 2.15, while the copy will stay on 2.14.
You will have to make sure you use the correct executable when playing the game though. The only problems while using the wrong Version should be bogus battle reports; the keyword here is should.
Hmm, the patch modifies (or adds) a file called army9.trs, though it looks like it does not affect Dom 2.14. I am not sure if it was present before 2.15, or if it has been added by this patch. If it is the latter, it will be fine, but there might be a problem or two otherwise. My guess is that this file is used to add some descriptions for the units of Oceania, as a few units of the nation are without description when playing the mod under 2.14. That is, however, a mere guess, so don't sue me if something goes wrong (of course, praise is welcomed if I am right).
