I'm running Affinity Photo 1.8.3 on a 2018 MacBook Pro 15" Touch Bar with 32 GB of RAM under macOS 10.14.6 Mojave. Printing is excruciatingly s-l-o-w. For the print dialog even to appear took 1 min. 15 sec.! Savor that number. It means after clicking File | Print... I had to wait 1 min. 15 sec. just to see anything happen at all. Since the default printer is not the one I use for printing photos, the first thing I do in the Print dialog is change the printer. After selecting the printer in the dropdown list I had to wait 1 min. 20 sec. before the new printer's name replaced the old one's. After that I changed the ICC profile and the print quality, then clicked Print. It took 1 min. 15 sec. until the Printing message disappeared.
Printing an exported .jpg or .tiff in Preview takes nowhere near as long. 2 min. 35 sec. just to change the default printer in the Print dialog!!!