WooCommerce shop admin getting slow

it seems that the only solution is to delete old orders.

Hey there,

The biggest problem is usually that too many orders are being loaded at the same time – you can change this by going to the Screen Options and setting the number of orders:

Link to image: https://cld.wthms.co/nLygFu

I’d also recommend checking through these tips:
https://woocommerce.com/posts/woocommerce-site-slow-fixes/

We haven’t heard back from you in a while, so I’m going to mark this as resolved – if you have any further questions, you can start a new thread.