Not the best. That does seem like a likely bottleneck now that you mention it.
Discussion
Still shouldn't take that long. A slow, old school hard drive should only take a week. SSD a couple of days.
I think you'll find it's failing and restarting.
The total download is about 800GB. It's the indexing that takes the time and works your drive really hard. Also uses heaps of RAM during the initial indexing.