Site extremely slow although good evaluations at pingdom, gtmetrix, etc

Hi, I have a quite annoying problem and really don’t know how to resolve it. The site loads way to slow (approx.. 10-20sec.). Different people worked on the issue, but weren’t able to get it fixed. As a result of their work, the evaluation of the website at pingdom, gtmetrix, etc is excellent. But in practice, it didn’t work out.

Website: https://www.europeansprintline.com
Host: bluehost

Someone able to help me please! Every advice is welcome.

Kind Regards,
Boris