In Cart Upsell uses an extremely fast, global CDN to deliver offers lightning fast. BUT, in rare cases, offers are still slow to appear.
We can fix this for you, quickly and at no charge. Just contact us using the "Contact Us" tab here in the help widget and we will set it up for you.
Because of the way Shopify auto-loads apps scripts, sometimes In Cart Upsell will have to "wait in line" for several seconds before it can load. If you find that this happens for you, we can put the script tag directly into your theme. This should make the offers load almost instantly.