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I don't think it's your theme causing your slow loading times. From what I've found, XOOPS site load times come back to three main factors;
1 - Fast & fat connection to Internet with an ISP hooked directly into the main Internet backbone.
2 - Fast server to serve web server, process PHP scripts and do requested queries on your MySQL database.
3 - Streamline the amount of content/images loaded on site as much as possible. From what I saw of your site there were probably 10 or so images on the main screen, of which some where quite hefty in size.
I've been having the same problem on my site to a lesser extent, and have so far things seem to be pointing toward a server upgrade. My suggestion would be to go into system admin -> preferences -> general preferences and enable Block/MySQL debugging and just see exactly how many queries are being run on your server on each site load, and also what the execution time is.