I don't trust HD's at all. I've lost so much material in the past (and even very recent past) that I always, always put everything in the cloud now. I have a subscription for Google Drive, but you can also look at Mega or One Drive, iCloud, etc. Sure it costs money, but the HD's also cost money and they definitely don't last very long anymore these days.

Although I have to say that I also throw away a lot of stuff these days, because I can easily find it again online and after watching something a couple of times, I don't really need it anymore.

Another thing is compression. You wrote that some videos are over 2Gb for 15 minutes. That's insanely big and definitely not necessary. 30 minutes of HD (1080p) should easily be scaled down to around 900MB.

Seems to me that a bit of sorting would also be good. Once you have a system in place, you can add all new stuff in that same folder structure and you can easily spot dublicates.

Hope it helps.