If page has 15 requests and needs data from all of them to work correctly, then with 20% failure rate you are suddenly close to 100% non-functional page from the user perspective.
A technique we've used to deal with this situation: in the overloaded backend (that has to reject some percentage of incoming requests), group the incoming requests by the parent request (the one with the 1:15 fan out) and reject according to the parent request. One way to put it, simply (though somewhat inaccurately), would be: reject 100% of traffic from 20% of users, rather than 20% of traffic across all users (causing essentially full failure for all users).
We typically implemented this by propagating an ID of the parent request down to the backend. I'm simplifying a lot in this description (e.g. have to deal with the parent requests landing on different backend tasks; also rotate the IDs gradually to introduce some fairness).
This is a pretty ancient thing as far as the FE goes: https://www.stevesouders.com/blog/2010/06/01/frontend-spof/
But that of course begs the question--why is the frontend retrieving all these data from 16 different endpoints instead of just one? It would be less overhead (http, auth, serialization, compression) to just serve it all in one request even if the http layer needs to fan out 15 rpc calls... this is why we can't have nice things.