First thing I did was to test the site, and - especially seeing as I’m looking from about as far away as possible - it doesn’t seem to be that slow. A re-run of WPT shows a very different picture:
This is showing a poorly performing http to https forward, and slow ssl handshaking. At a guess, you’re using a shared server package, and it’s a bit overloaded. I expect you’ve had a few strong words with your provider and/or installed a full page cache ( ah, yes, I see a rocket footer ).
Are you selling worldwide? If so, then I heartily recommend not hosting in the UK - Torquay even more so ( if that’s where their data centre is ). Speed is of the essence with eCommerce sites, so I’d get the static resources delivered by a geo-aware CDN service ( remember, your DNS provider needs to be geo-aware too, so check with them that it is ), and that’ll leave a nice small html framework to be delivered directly. Given the size of the pages, this won’t be a large cost ).
Just one comment… the product price. It tells me it’s in $, but I don’t know whether it’s NZ$ ( because it tells me it knows where I am in the checkout ), US$ ( it’s a .com ), and it also converts it to UKP on the last line of the checkout data. It would be less confusing if a little banner let me know which currency was in use.