I don't have an answer for your problem but I'd be very interested in implementing this on my site. Any chance you could share an example?
first of all you have to check if the problem comes from the connection through Eloqua's URL or the processes inside your website.
When you click the button, then the blind form post the data to Eloqua's database, so you have to detect if the problem comes from this data export or from your internal website circuit between the click action and the post data.
I suggest that you try Inspecting Element in Chrome (right-click on the page > Inspect), then go to the Network tab. Finally, refresh the page and you will see how long each element of the page takes to load to see where the time delay is occurring. More help can be given once this information is ascertained.