Why does firebase + ionic hang to send coordinates between users?

Question

JavaScript

Problem: if there are more than 40-50 users in the database (firebase), then terrible lags begin. just for any queries to the database. If there are fewer users, then there is no problem.
This is what the user looks like in the database:

What happens:
coordinates come to connections, and those users to whom they need to be given are in keys (I go over keys , take the user's key and use this key to access him and put the coordinates in connections)
PS. firebase free version, limited to ~100 simultaneous connections, which is out of the question, because at the same time even 3 people have not yet used