The issue was your search subscriptions. You had created 79 search subscriptions. Therefore, everytime you loaded the category, you performed at least 79 individual and complex searches on the database. That is what was taking so long to load.
I re-created all of your 79 subscriptions into 1 subscription. You can see it set up under the "TEST" category in your store. It still takes a couple of seconds to load because the query is still quite complex, but there is only 1 query instead of 79.
Check it out and let me know if you have any questions. I used most of what you used but set up the price filter to quickly and efficiently filter out products that, based on price, do not match your category niche.