Public and private IPFS gateways both connect you to the same IPFS network, but public gateways are sensitive to traffic since there is only a limited amount of bandwidth. If lots of people are using the public IPFS gateway in your area, your content will load slowly.
Dedicated Gateways are focused on performance, getting your content distributed and shared to an audience without any slowdowns. Faster content retrieval, customized URL paths, and tighter control of who can access your content.
Read more here: How to use Dedicated Gateways