website slow with theme with large cart

Hi when we get to over 33 products in our shopping cart our entire site slows right down where customers are complaining and abandoning their orders.  I have performed troubleshooting and found that it only happens with B2B King & our theme enabled. If we switch to default theme it doesn't happen.  The theme developer is telling us its the plug in's fault. How can we get both to work together?   Our theme is the Zorka shop theme

Thanks

Hi thank you very much. We have instead decided to ditch the theme as their support was not helpful for things we need. Thank you for your response on this we will also try the update on our current site while we are rebuilding our theme on our staging site. Thanks again for your support