I've been running into the following issue with custom lower 3rd CG titles:

1. I create a template for animated lower thirds using client provided .png sequence for the animated background. This is set as an image sequence on layer 1 in GT Designer Advanced.

2.Layer 2 is the text of the title. This is created in GT Designer and animated with reveals, timed to match the .png sequence reveals.

Once the template is set I then create all of the titles required for a show. These titles are then added to the vMix show.

This process is simple and not where I'm having issues.

This issue I'm having is that once I load the titles into the vMix show, the system memory resources are quickly exhausted. I'm currently running a test show with 3 titles and vMix is using 9G of memory. 3G of system memory per title seems excessive. Is there a more memory efficient way to accomplish lower third titles?

The issue you are facing is related to GPU image processing. Every single frame is in uncompressed format in the GPU memory. One 1920x1080 frame is about 8MB.
Now if you have 600 frames, that is 600x8=4800MB of GPU memory used.

There is no way to compress them. Only way is to lower resolution. If you do not want to lose quality, export image sequence only of needed part of the frame not entire 1080p.