Photos upload to iCloud is very slow (1 photo per minute) - is there any way to speed it up?

I have a photo archive with 350,000 photos. I recently upgraded my iCloud account so I can store them all in Photos, and started loading photos. I have loaded the first 100,000 into Photos, and it is taking forever. Some observations:

• photoanalysisd and photolibraryd ran (off and on) for about 4 days (CPU utilization in Activity Monitor was dominated by these two services and totaled about 50% this whole time - that's 1/4 of total available CPU)
• During this time, photo upload was about 1 per minute (Network activity in Activity Monitor jumped to 1MB/sec for a couple of seconds, then dropped to 0 or near zero for the rest of the minute). After the first day I turned iCloud off, since that seemed to make these services unstable.
• once I babied photoanalysisd and photolibraryd to the point that they won't run anymore, I'm getting sustained uploads in the 500-900KB/s range. I have 750GB of photos; this will take about 10 days at this rate, for 14 days total.

First question: photoanalysisd and photolibraryd seem super finicky; the only way I found to get them to run (as evidenced in CPU utilization in Activity Monitor) was to turn off iCloud for Photos, reboot my Mac, open *only* Activity Monitor and Photos, then disable sleep. This would get them to run for a day or so at a time, then I'd have to reboot to get them to start again. Photos itself showed a progress bar stuck in the middle and flashed its "Analyzing / Optimizing / Whatever" message this whole time. Is there a way to tell these services to please use all of the CPU to speed the process up?

Second question: is the slow upload speed expected, and is there any way to speed it up? I have FIOS, and my network readily supports 15MB/sec uploads (that's what I got when I made the backup). My computer is plugged into wired ethernet, so WiFi isn't an issue. Having to baby this process along means I don't want to use my machine for anything else, and not using it for two weeks is ... problematic.

System:

• macOS Catalina Version 10.15.4
• MacBook Pro (13-inch, 2017, Four Thunderbolt 3 Ports)
• Processor: 3.1 GHz Dual-Core Intel Core i5
• Memory: 16 GB 2133 MHz LPDDR3