Any update on this?
One of the main problems seems to be the huge avatar images. They are displayed quite small while their size is big.
/activity (not mobile, here the image sizes are fine)
3.626 bytes compressed with factor 9 (PNG)
24.843 bytes "data:image/png;base64,iVBORw0KGg..." (JSON uncompressed: 38.031 bytes) - displayed as 29x29px²
13.596 bytes compressed with factor 9 (PNG)
28.152 bytes https://community.jivesoftware.com/api/core/v3/people/32109/avatar - displayed as 48x48px²
21.398 bytes compressed with factor 9 (PNG)