I've had this as well the performance of v17.x using levels isn't good compared to the previous version. I had to increase my hardware spec to get basic levels to work. try upgrading to 17.3 as it does have sone performance improvements.
At the moment I'm steering clear as much as possible from levels until they sort it out.
I have with similar results in performance to levels as it's grouping across rather than down the workbook. also tricker to implement as need to be careful what you use as sheet names in terms if length and symbols used.
Tbh I'd sooner not have to worry about these things but it's where the solution is at the moment so I'm having to scale back on what I can deliver until it improves.
I did notice an improvement moving to later releases. Levels will impact the time to generate reports so ive used sparingly in my reporting.
Is your app you are using optimized for nprinting?
I.e Only data and charts required for nprinting included.
What's the size of your app and what's the spec of your server?
If you create a template with many nested levels or by inserting into levels fields with a lot of different distinct values you could experience performance issues.
This is because each value of a level is a filter. So Qlik NPrinting applies that filter, export the data and go ahead with next value. This requires time.
There are many conversations here about performances and how to increase them. For example Re: Good performance of Nprinting with Qlikview
Check also the help site page https://help.qlik.com/en-US/nprinting/February2018/Content/DeployingQVNprinting/Performance.htm
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