Lpr vs print dialog

I have a network attached Epson ET-2550. On my Mac Pro running MacOS Sierra, I have configured that printer. I have also set up a CUPS printer definition, with my preferences for that printer, when I want a high quality printout. When I want to print out a high-quality PDF, if I use Acrobat Reader or any other PDF editor via print dialog (Command-P) everything is fine, once I choose my print options and hit "Print". If I go into Terminal and issue "lpr" for the same file, I wind up with an equal high-quality hard copy. The difference is the printing speed. Using the print dialog from a Mac application is an order of magnitude faster than with the Terminal lpr command. Does anyone know what the Mac print dialog may be doing differently that would account for the speed variance? Thanks in advance.