Excessive usage of cloud functions is slowing down my app , whats the alternative?

I have made almost all my requests through cloud functions and jwt , due to security fears of a user editing a field he is not supposed to .

This unfortunately means instead of the almost instant direct call , sometimes the function takes up to 20 seconds to load (when it hasn’t been active in a while)

Regardless even normal functions usually take 4-5 seconds and it’s not a complexity issue it’s rather the usage of the cloud .

What’s the alternative to all this ? (Thats also secure )