Shopify Speed Optimization - 0ver 3000 items

I have built [login to view URL] over Shopify and because we have over 3000 categories/sub-categories and thousands of products, the store does not perform fast enough which reflects badly on sales. As you know, customers have no patience and our business suffers due to slow site performance, Now, I have previously hired people who have tried to fix this issue by implementing various tools and techniques and while it improved the speed a bit, it did not make any significant difference and we continue to face this problem, Is there any way to hook up Dedicated Server to a Shopify Store besides Enterprise option? Or maybe you know of any effective tools that can make it possible? Also, what would be your estimate to MOVE the site to another platform the way it is now? to include all of the categories/sub-categories and move products the way they are since many are listed as variations, I would LOVE to keep my store with Shopify though, however, the only way it could happen is if we can make it load instantly and I am looking forward to your professional opinion and update, I can also give you access to my Shopify Admin if necessary just so you can take a look at what has been done previously and see any potential going forward, Thank you and Have a Wonderful and Safe Day!