PHP Core Proramming

Hi

I'm looking for a PHP Core expert to check my website code due to some pages loading slower than others. Please only contact me if you have over 5 years experience. My web address is poundmad.co.uk please click the link then enter a warehouse to see the delay. The website is fully optimised and I've checked the servers performance so it's not that.

https://poundmad.co.uk/product/select-warehouse.php?ctg=TOYS

Many Thanks
Stevie