Thanks for the replies!
Lion in the Stars: I'm working on it, I have two buildings that are done and a third that is almost finished. I plan to release the range when I have five items. However, it won't be the same buildings, as there are things that I can't pull off in 6mm that I can do in 15mm. More room for details and such.
Due to some last minute changes at my job, I'll end up with two weeks of vacation in July where my wife will be abroad, and I'll be all alone, with nothing to do but my hobbies, some TV series and beer. Oh pity me. So hopefully those weeks will be enough for me to get buildings #4 and #5 done.
Shedman: Yes, I do think these are passable both for Korean buildings, and for periods after 1600, especially for rural areas. Japanese architecture has two very clear influences that came from two places an clashed on the Japanese islands. The first is the Chinese/Korean style of building houses, and the second is the South-East Asian/Pacific style. The South-East influence is clearly seen in the way that traditional Japanese houses are often raised from the ground. Today this is still seen in the "genkan", a small entry area that is on street level, where the rest of the first floor is raised a few inches. You can see this in this 28mm house I built:
However, this is kind of hard to pull off in 6mm resin buildings. So instead, what you mostly see in my range are buildings that lean more heavily towards the influences of Korean and Chinese architecture. Both ordinary houses and Buddhist temples of Japan are quite similar to these.
You see more distinction between Korea/China and Japan once you move toward military buildings, fortifications and Shinto religious buildings. For example, this Korean gate in the Gyeongbok Palace is very clearly a heavily Chinese influenced style that you'd never find in Japan defensive buildings, even though some individual parts (the tiles, the square stones at the second layer of the wall) are often seen in Japanese castles. The actual gate itself is just way different:
Another example is this, the birthplace of former president Kim Dae Jung. The main house is very similar to an ordinary Japanese farm house, but the smaller buildings on the sides would look unusual in Japan, as their walls are built up with small stones. In Japan, sheds like these would have wooden walls, or maybe even just be made out of thich sticks and thatch. The stone wall would also stick out in Japan, where you would see loose fences of bamboo or sticks.
If there was ever a good alternative for 6mm Koreans and Chinese for some Imjin battles I'd happily read up more on Korean architecture, but as for now I'm sadly not good enough at it to do more than point out where it's different from Japanese. Same goes for traditional Chinese architecture.
Sizewise, I think they should be ok for 10mm, though I don't own any. Actually, just as you, I'm quite fond of 6mm buildings for 15mm wargames as well. The smaller footprint means that you can fit more than a single house without completely crowding the table. But this is a personal opinion, and some people think that it is jarring to have buildings of a different scale.