Very slow scheduled report execution

[Rosanero4Ever]

Hi all,

I'm using IBM Cognos BI 10.2.1 and I scheduled three report. When I execute these reports from IBM Cognos Connection the execution is very fast, but If I schedule these reports the execution is very very slow. Today, I scheduled them at 11:00 AM and they are still in execution status! (so, after 3 hours)
The server has 8GB of RAM and it is used mainly for schedule reports (there are 92 schedule tasks)
In the meantime I required a RAM upgrade to 16GB because If I reboot the server the performance returns high.
What do you think about this problem? Is it due only to memory?
Many thanks in advance
Regards