Very slow user registration form, stops working/stalls

Our site, [login to view URL] has a registration form for users ([login to view URL]) where they have to upload a picture of a government ID. The form is then uploaded as a pending vendor to our site in order for us to verify their identity. The problem is the upload time. For some unknown reason, our upload time is horrendous, with a picture taking on average of 15 seconds+ (for newer phones with larger image sizes, this process completely stops working all together.) This problem is further exacerbated by users using mobile phones to upload, which causes the form to freeze instead of transitioning to a checkout. This is severely impacting the number of users who sign with our site, and we are desperate to pinpoint/fix this problem. We're seeking help to fix the poor upload time of the registration form (we think its the image upload), whether it be through switching hosting companies, or editing our theme/registration form. We are desperate to find a fix to this solution.