I have the same issue, but mine is at 5 GB. The "Other" problem was never really fixed, it just clogs up System now. Corrupted data, incomplete downloads, and god knows what else gets stuck there indefinitely. Deleting apps with possibly corrupted data MIGHT reduce it though
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I downloaded GTA, but the download failed twice. So the game took up its space and made my Other extremely high back on GDR3. Deleting the game cleared up a lot of Other. Just recently I knocked off 1.5 GB from System in 8.1 by connecting the phone to my PC and deleting all folders in the "Video". My phone said there was 650 MB of data from Video in Storage Sense, but I had no offline videos from Xbox Video on my phone, I deleted them a long time ago. The data must not have been wiped completely... All the folders in Video were empty, but when I deleted them, I got my 650 MB back and 1.5 GB from System!