Dos documentos.
Você pode passar
batchSize
com AggregationOptions
na versão Spring Mongo 2.x Aggregation aggregation = newAggregation(unwind, group).withOptions(newAggregationOptions().cursorBatchSize(100).build());
Com tamanho de lote padrão
Aggregation aggregation = newAggregation(unwind, group).withOptions(newAggregationOptions().cursor(new Document()).build());