Using Sketch, I have developed the following workflow:
- Create combined paths where possible.
- Flatten all paths.
- Export as SVG.
- Run through SVG Optimiser using aggressive settings. I choose to not use relative coordinates because of my specific needs, but relative coordinates save space. Use them if you can.
- Upload the resulting vector. I often am able to gain 60% optimization through this process (depending on number of nodes and complexity of the artwork).
PS: I tried importing your vector code “initial output” to compare the results using SVG Cleaner, but it appears to be invalid. Both Sketch and SVG Cleaner have trouble reading it and produce no results. If you can send me your original heart file, I would love giving this a shot and seeing how well my process stacks up. :) Thanks!