Open the Settings Editor and go to: . See setting [Use PDF XObject optimisation].
XObjects are objects in PDF that can be used on multiple pages of a document. APPE can optimise the interpretation of XObjects by caching an intermediate representation of the content. Because this involves some overhead, by default the setting [Use PDF XObject optimisation] is switched off. Setting [Use PDF XObject optimisation] can be switched on to improve the performance of variable data printing (VDP).