- Have you any other ez install on the Linux system, or is it the first time you host ez on this server?
- If no try to increase the max php memory and max_exec (60/60), in php.ini. - If this doesn't work you can try to use a php accelerator. I recommend eAccelerator http://sourceforge.net/projects/eaccelerator
The source of your problem can simply bee that your server provider host too many sites on a server. Personally I recommend hosting EZ yourself on a Linux system or on a dedicated Linux server, because then you avoid many problems.
Try to enable DebugOutput in site.ini.append.php. This can be also permission problem. Make sure that you set right permission for var/ settings and design dirs (usualy 777). With out this eZ publish can write cache files so every loading takes a time.