Your concern is likely a preview issue. Viewing photos at less than native resolution at any percent other than 25, 50, 75 or 100 will cause artifacts. Change the program window’s zoom from “Fit” to one of the above.
Also if you plan on any pan/scan, do not select “Scale to frame size” as Premiere will create (in media cache) a new version version of each photo as your Project Settings resolution. This is like generational degradation and for Jpegs a quality hit..