Taking too long after click in “buy” button

Hi There,

I am having a issue on the time the sidecart is taking to go to the checkout page.

After a click in the “Agende e pague agora” button, wich means ” go to payment”, is taking about 15s to go to the checkout page.

In the website, the flow could be:

1- Open https://www.isalab.com.br
2- Click in “Covid-19” on header (we sell Covid Exams)
3- In the PCR Express card, click in “Agendar”, This will open the side cart
4- Wait

Is there any idea on how to fiz that?

Thanks in advance

The page I need help with: [log in to see the link]