Classifying Category takes 10 minutes to load in HMC

Hello there!

We have a Classifying Category which includes 253310 products and it takes 10 minutes to load.

If it would only be the "Category Structure" Tab which needs 10 minutes, then I would say this is OK, but it already needs 10 minutes for the first tab - or any other tab where the products are not even displayed.

Can you help me there? What could be the reason and how can I fix it?

Thank you for your time in advance,

Nic