Make requests with nested fields faster

Help
1

I have a type Course in my subgraph Course.
To get all my courses i use this query:

Courses {
  _id
  title
  etc
}

Everything is fine with this
But now I also have another subgraph named progress
In this second subgraph I extended the Course type to add a nested field named totalProgression, which gives me the users progression on a course:

extend type Course {
  totalProgression: Int
}

And now I can make my query like this:

Courses {
  _id
  title
  totalProgression
}

This works, but it takes a long time.
That’s because for each course I have to get the totalProgression, and to get totalProgression I have to make a mongo request.
If I want to add another nested fields from other subgraphs (for exemple I want to add the students field in the Course type, students that I will get from the User subgraph) it will take even more time.

Is there a way that I can make these queries faster without having to merge all my subgraphs ? Like a way to make one request to get all the totalProgressions and then putting them in the courses, instead of requesting them one by one ?