I know this review is a few months old, but I'm curious as to why it was done in Raid 5/6 as opposed to SHR, as I would assume most people would use. I'm guessing that it is because Raid 5/6 are common to all brands of raids while SHR is proprietary. It would be nice to see what the benchmarks are for it though.
And to answer some other user's questions about the use case - I'm currently considering this NAS for my photography business. Currently there are only 2 users, but we have filled up a 4-Bay NAS with 3TB drives. Replacing said drives with 6 or 8TB ones is as expensive if not more than getting this 1815+, and there is no room for expandability. The plan would be to buy this, add extra 6 or 8 TB drives to the array, and if we ever fill that up then replace the 3TB drives. I know that's not an ideal situation, but it's the most cost-effective solution. Building a similar FreeNAS box would cost less, yes, but if anything went wrong our data would be unreachable until I had time to fix it myself, which there is no guarantee I could do despite me being pretty competent. I just cant risk losing that data.