10-15 koi in a 375 gallon pond is not feasible. It's fine when they're 3 inches long (barely), but remember that Koi get BIG very fast. I predict we'll be hearing you talk about going bigger any week now....LOL!
i have about 20 left that are hovering around 1.5"
and im pretty sure i got a rid of that virus
the 2 koi are doing great in there
i am waiting for it to get warmer to actually tell