Hello,
Due to GTmetrix result https://gtmetrix.com/reports/www.interiorflair.co.uk/TUIF0lEy , please follow the suggestions from these articles:
https://varvy.com/pagespeed/leverage-browser-caching.html
https://varvy.com/pagespeed/defer-loading-javascript.html
http://www.elegantthemes.com/blog/tips-tricks/optimize-images-for-your-wordpress-website
http://premium.wpmudev.org/blog/10-best-image-optimization-plugins-to-speed-up-your-wordpress-site/
Also you can use some additional plugins for compression, image optimization (WP Smush etc.) and Javascript / CSS Minifiers. These can optimize and speed up your website.
Yes, you need to set 5000 or even 10000. Also, you may try to clear Object Cache in your cache plugin settings.
Regards,
Rose Tyler.