Geting smaller buckets from GoogleFit doesn't work

Question

I am trying to get GoogleFit data with buckets of 15 minutes for the last 2 weeks. But for some reason the call to the HistoryApi does never finish, even if I wait some minutes. When using 1 hour buckets, it returns pretty fast. Are there any limitations I just didn't see?

My plan would be to get 15 minute buckets for the last year or so, but if not even 2 weeks work that's going to be a problem...

What I have so far: I set up my GoogleApi Client like this:

        mClient = new GoogleApiClient.Builder(mContext)
            .addApi(Fitness.SENSORS_API)
            .addApi(Fitness.HISTORY_API)
            .addScope(new Scope(FITNESS_ACTIVITY_READ))
            .addConnectionCallbacks(
                    new GoogleApiClient.ConnectionCallbacks() {
                        @Override
                        public void onConnected(Bundle bundle) {
                            fetchHistoryData();
                        }

                        @Override
                        public void onConnectionSuspended(int i) {
                            // Here I'll handle that case
                        }
                    }
            )
            .enableAutoManage(mContext, 0, new GoogleApiClient.OnConnectionFailedListener() {
                @Override
                public void onConnectionFailed(ConnectionResult result) {
                    //Here I'll handle that case
                }
            })
            .build();

And then I try to fetch data like this:

    final DataReadRequest readRequest = new DataReadRequest.Builder()
            .aggregate(DataType.TYPE_STEP_COUNT_DELTA, DataType.AGGREGATE_STEP_COUNT_DELTA)
            .aggregate(DataType.TYPE_CALORIES_EXPENDED, DataType.AGGREGATE_CALORIES_EXPENDED)
            .bucketByTime(1, TimeUnit.HOURS)
            .setTimeRange(startTime, endTime, TimeUnit.MILLISECONDS)
            .build();

    Fitness.HistoryApi.readData(mClient, readRequest).setResultCallback(new ResultCallback<DataReadResult>() {
        @Override
        public void onResult(@NonNull DataReadResult dataReadResult) {
            handleGoogleFitData(dataReadResult);
        }
    });

which works perfectly fine, but when I go ahead and change the bucket time to .bucketByTime(15, TimeUnit.MINUTES) my onResult will never get called. I also noticed the same when having 1 hour intervals and going back 1 year.

Is this a limitation of Google-Fit? I at least didn't find any documentation about a limit like this...

I also sometimes get a callback of a query fast, sometimes it just won't ever return. Any ideas about that?