A few pages is a pretty vague concept, moreover it is what you have on those pages that matter most when it comes to performance. The processing time (consumed memory as well) depends heavily on the complexity of the report layout, data calculations (aggregates, conditional formatting), the rendering media, and the size of the generated document (in pages). In this line of thoughts handling such reports requires powerful CPUs, and enough memory to handle all those operations.
We're not sure whether you want to ask for actual help on how to optimize your report (have you reviewed our suggestions in the other threads you've encountered?) or you just want to voice your opinion here. Either way, without a runnable sample project on our end, it is very hard to give appropriate advise especially when it comes down to making something work faster. Sending us a sample runnable application is usually the fastest way to get to the bottom of a problem and suggest how to optimize it or confirm it as an issue that needs to be addressed on our end.
As for your second question, unfortunately there is no way to cancel a report from being processed/rendered once the process begins. The web is stateless, i.e. the server is not aware of what the client does, so what happens is: you start the processing and it is performed on the server until ready. This process continues independently on whether your browser is still there waiting for the report to appear or has been closed during that period.
Telerik Reporting is an embedded engine which means that it is part of your application (not a separate one). If you can figure out a way to stop your application at a certain time (i.e. elapsed time or taken memory), this would stop the report processing as well.
All the best,
the Telerik team