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Then try installing W3 Total Cache or WP Super Cache.

Maybe the problem is that you have too many plugins, or some of the ones I've installed slows down the loading of pages, check.
Let me know.

What's your problem with your website?

For activate REGISTRATION go to settings "General" and select the option "Anyone can register".
Let me know.

Yes, it is possible to record two accounts, but with different email from that used for the first site.
Therefore you must record a new account.