When you see literature from a manufacturer claiming 15 cases per minute, keep in mind that the speed is rated for a specific box size. Usually the smallest size box that the case erector can process.
This same case erector will have lower outputs when processing the largest size box the machine can handle.
So, the bottom line is this...the output of a case erector is the net result of the machines ability and "YOUR" carton sizes. Published speeds should be considered as a barometer, not the end result.