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difficult to say. Most of the time speed aka performace issues are due to the configuration and resource availability of the server the site is hosted on. Performance depends on available memory, number of open connections, session durations, concurrent users, number of active processes on the server, availability of CPU time, available bandwidth, installed server extensions, load balancing configuration, caching infrastructure, activity of other sites on the server... The list probably goes on for the initiated.
The script running on the server is but one factor. It could be because of XOOPS 2.2.x, but from the problem report 'my speed is gone' it is rather difficult to make a decent analasys.
Check with your hoster to find out what is causing the dramatic reduction of speed.
Herko