Hi, WP is a good CMS but is open for too much attacks Js DB Injections (security holes) , this can slow down your performance , this days there is a plenty WP plugins, so my suggestion will be to start installing security plugins like "All In One WP Security & Firewall" just search google for "wordpress security plugin +free" after that search for wordpress store plugin free or themes no codding need it , but most important think for your performance would be your hosting (shared or not), if you have dedicated server would be good