We typically use QGIS as a viewing engine only, if you let postgis do the heavy lifting it's a beautiful setup, especially with a tuned dB and a indexed clustered postgres table
That fixed it, thanks! Looking at the manual, there is a tip that tells you to turn that on, otherwise it will read the entire table to characterize the geometries... It's a bit mad that the default behavior has it querying potentially gigabytes of information across the network every time you open the app and click a dropdown, with no progress bar. But it's definitely the type of app where you need to read the manual, and it says so right there.
It should only do it once per table but if you are dropping and creating tables often it will be making the DB have a heavy workload
I think theirs an assumption within the geo community of read heavy workloads but I could be wrong