What hardware are you running it on? I set mine up originally on a raspberry pi 3b and the web interface was very slow, but upgrading it to a RPi4 with 4GB RAM made a massive difference. Though I suspect some of that was that the data and database were being stored on an external SSD in both cases, the RPi4 had a usb 3 interface and dedicated Ethernet, but the 3b had a single USB 2 bus to share between the Ethernet and SSD.
If you're handy with Linux you can configure it to only use the working part of the monitor: https://superuser.com/questions/1305338/linux-distro-how-to-use-only-part-of-monitor-for-display https://duckduckgo.com/?q=linux+use+part+of+broken+monitor&t=fpas&ia=qa