Hello,
Please try installing this plugin to test if any of the current plugins you have installed are causing the site to be slower. If WC Vendors Pro is the culprit, please provide screenshots of the info and data so we can see what may be causing our plugin to slow your site. My guess is that it is actually another plugin, like the chat or something else. Nevertheless, let us know, and show some results so we can see:
https://wordpress.org/plugins/query-monitor/ will show you HOW LONG a query took, and thus, tells you what the actual problem is. If the queries are not “slow” then the hosting is the issue and the website is fine.
Also, make sure your database is clean- if you have been doing a lot of testing and revisions, your database may need a sweep to get rid of all of the post revisions and cling-on crud after testings plugins, page revisions, etc.
ETA: Changed plugin suggestion. Thank, Ben! hehe