Hi Helmut,
Hope you doing great.
Reviewed your requirement. Your site is already in Shopify and other few js and css are using Shopify CDN which are already faster but speed test display them slow because url is different, there are few other things which we can fix like js and css compression which will also increase the speed and few files are natively belongs to Shopify which we cannot change so they will not fix but rest we will fix. And it will take a day to fix and test the site. Please add me on skype: cis.brenda or mail me at brenda.cis40@gmail.com. Please let me know your inputs on this as I am ready with the quote.
Regards
Brenda