Nagios 4.x showlog.cgi superslow

Hello.
I've upgraded nagios from 3.5.1 to 4.1.1.
I've noticed that showlog.cgi is now überslow, it hangs my browser for 15" or even more!
the problem is with files "nagios.log" and the daily archived ones... with the older version of nagios those were ~100KB and now their size is about 100x bigger!

those log files contain a lot of info about wproc, like:

[1448633087] wproc: Core Worker 783: job 90576 (pid=23636): Dormant child reaped
[1448633104] wproc: Core Worker 783: job 90591 (pid=23731) timed out. Killing it
[1448633104] wproc: CHECK job 90591 from worker Core Worker 783 timed out after 30.01s
[1448633104] wproc: early_timeout=1; exited_ok=0; wait_status=0; error_code=62;
[1448633104] wproc: Core Worker 783: job 90591 (pid=23731): Dormant child reaped
[1448633114] wproc: Core Worker 781: job 90594 (pid=23756) timed out. Killing it
[1448633114] wproc: CHECK job 90594 from worker Core Worker 781 timed out after 30.01s
[1448633114] wproc: early_timeout=1; exited_ok=0; wait_status=0; error_code=62;
[1448633114] wproc: Core Worker 781: job 90594 (pid=23756): Dormant child reaped
[1448633119] wproc: Core Worker 782: job 90598 (pid=23782) timed out. Killing it
[1448633119] wproc: Core Worker 783: job 90598 (pid=23783) timed out. Killing it
[1448633119] wproc: CHECK job 90598 from worker Core Worker 783 timed out after 30.01s

is it possible to filter out those event messages so they don't appear in the log files? I've played with nagios.cfg file but I cannot solve it by myself...
thanks a lot for your help.
regards,
Federico