Improve performance according to Google Page Speed Insights

Dear community,

I just started “playing around” with this theme and figured out that the site performance according to Google Pagespeed Insights (https://developers.google.com/speed/pagespeed/insights/) is bad especially for the front page on mobile devices. This is even the case for the demo page (https://developers.google.com/speed/pagespeed/insights/?url=https%3A%2F%2Fthemes.getmotopress.com%2Fpalmeria%2F).

From what I see, this might especially be related to the fact that the theme suppresses loading child page thumbnails/featured post images at a reduced size (function palmeria_child_pages_list temporarily adjusts the srcset calculation using palmeria_calculate_image_srcset_meta). This causes the featured post image to be loaded at full size (i.e. usually much bigger than the device width).

Any idea how to fix this properly?