I have asked Qlik the same question few times. They said that NPrinting 17 may be slower than 16 and that they are working on performance improvement.
I understand frustration but reality is that you cannot do much more (obviously apart from all the other things i suggest to do with any aplication serving data for NPrinting).
As NPrinting 17 is completly different tool than NP16 you cannot compare performace.
I know they made an improvment in 17.3 from 17.1 and 2 which were at times for me unusable.
Im sure they are looking for more improvement in each release but I have adjusted my expectations of what I can and cannot do with my reports. I try to keep them as simple as possible at the moment to ensure delivery and content that is usuable but without the bells and whistles.