specialist in pump installations?

Please help, I have purchased two different pumps, and I don't want to get the 3rd one wrong too. I need 5 litres in 15 seconds in order to operate this smart toilet: https://uk.homary.com/item/modern-black-smart-onepiece-128-gpf-floor-mounted-elongated-toilet-and-bidet-with-seat-42877.html I live in a flat in Central London - old building, water pressure is not good. Can someone please advise me which pump type to purchase. Thank you!