The plugin has to wait for a response from Salesforce before it can render or redirect.
That might be a factor, but it’s one neither of us can control.
Your server/theme/plugins are a factor outside the plugin’s control.
I can tell you that the plugin does very minimal processing, uses WP core functions for all external communication (so it’s unlikely SF being slow as it would likely time out) and … submissions are nothing but speedy (like nearly instantaneous) in all my testing.
That leaves something unique to your site/server, which is not covered by our free support policy. Sorry!
We do offer premium support for site-specific issues:
https://luminfire.com/support/premium-plugin-support/
