WooCommerce slow POST ?wc-ajax=get_variation

My website is running slower then usual lately and especially switching variations on single product pages takes ages to load.

https://www.lindenbedrijfskleding.nl/product/overhemden-blouses-tuniekjes/dames-blouse-regular-fit-6515-1120/

On my network inspector it takes 5.5 seconds to load the variation and the variation image. I don’t know how this is possible and it’s only happening since a week or so.

Here is a screenshot of the network inspector:
Link

I can’t locate the source of the problem and already tried deactivating plugins.

Anyone please help me!