Damon Chaplin these skins were designed several years ago, when boxes were slow. Oh the joys of my zgemma S2 :). So at the time they were optimised.
Which is why the code was all templated. At the time all the pngs were compressed.
The JPGs were considerably smaller than PNGs so for memory size this is why they were used for some backgrounds.
Since then, all the image teams builds have nearly doubled in size. Bloat, bloat and more bloat.
Also since then we have moved on to python 3, which despite its claims, was never as fast as python 2 builds.
We also have 1080 skins now as the norm (which doubled all the size of the graphics), and now also UHD screens for dreamboxes.
So everything is getting larger and bulkier and using more memory.
All my skins have very little tweaks over the last few years as my primary focus switched to my plugins and not skins.
But I am giving them a once over at the moment. No harm making suggestions and improvements. But any improvements or tweaks have to work on all oe-alliance images. And tweaks have to be in the skin files, not the enigma2 core components. That isn't my issue.