How long is "too long?"
Are you by chance printing with overlays? If so, and if the printer is merely an AFP printer, the iSeries must build a bitmap of each page being printed and send it to the printer. If you use IPDS, with an IPDS-capable printer, the overlay is sent to the printer once, and married to the variable data as each page flits past-- must faster! There are stand-alone IPDS interfaces-- one is a device much like a jet-direct box for a single printer, another handles 3 printers. Unfortunately, I can't recall the manufacturer's name at the moment!
Of course, this difference in speed mostly affects remote locations with long communication lines. Generally, locally-attached AFP printers can handle limited amounts of overlay traffic without slowing things down too much.
If the device is a network printer (ie it has its own IP address) it should work better than a remote outq. Remote outqs don't have some of the controls to start printing and a certain page, hold and restart, etc. (I think multiple copies may be affected as well, but don't quote me!).
Paul E Musselman