Slow performance

I’m using Print-o-matic to print an archive list of custom post types: list has 25 items in a table. The bare rendering of the page appears instantly, the print preview screen then takes a minute to load. What can I do to improve the speed of the preview? It makes the plugin unworkably slow at the moment. Thanks.

https://www.ads-software.com/plugins/print-o-matic/