Have you successfully streamed using this computer before? That is an old CPU for rea-time video encoding, and I suspect when you added chroma-keying, you simply have gone beyond that CPU's capability
I had a MUCH simpler OBS setup, using same gen CPU and failed. Could I get it to work a year later with what I know now.. probably. but with a really limited setup. So, by being attentive to CPU load each setting filter and effect has, and monitoring your hardware utilization (CPU, GPU, RAM, disk I/O), etc - you should be able to get streaming working. But I'd caution you against expecting your stream to look like that created on much more recent and powerful systems (in terms of filters, effects, layers, etc)
If upgrading PC isn't an option, then expect it is likely you'll need to learn to optimize your Operating System and OBS for livestreaming for an under-powered system
Also, you are creating work by having a different base and output resolution
15:29:48.802: base resolution: 1920x1080
15:29:48.802: output resolution: 1280x720
Hopefully someone who knows more than I can point to something specific in your setup, but I wouldn't count on it
