I'm currently switched from an older Octopi to the bullseye version with the new camera stack on Raspberry 3b+. Before I switched, Login to Octopi was also slow, but I got my multicamera setup running. After switch to bullseye Octopi, I get barely my cameras running. Snapshots not always working, sometimes I can't switch between cameras. Even with optimze my camera setup (FORMAT=MJPEG, FRAMERATE=5 ...), it doesn't working well. Sometimes I was not able to save new settings. I tried a different SD-Card or a Raspberry 4, instead my Raspberry 3. Nothing helps. The new camera-streamer uses only 1% even during streaming. There is no process which consumes too much CPU.
My problems were soved by setting the scaling_governor to performance. Octopi is now running much better.
Add this at the end of /etc/rc.local before exit 0:
echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
I know it might be a too much, but I hope someone has better parameter for the CPU govenor. I'm using a Raspberry case with much openings for air and heatsinks (no fan). My CPU is running on 54 Degree Celcius. This setting might be not good for a closed case without heatsinks.