Performance problems scroll search

Hi, I am using elasticsearch 1.7.
I have daily indexes when I do a search with scroll, with tree months de elasticsearch became too slow or not responsive.
Take a look some graphs that I printed from Marvel from data nodes

3 Master
Java Heap: 5GB
2 CPUs, Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz
RAM:7,5GB

3 data nodes
Java Heap: 8GB
2 CPUS : Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz
RAM: 15GB

2 client nodes
Java Heap: 5GB
2 CPUs Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz
RAM: 7,4GB







What is the best approach, increase number of machines? Increase the machines sizes? change architecture of my solution?

My search

{ "_source": { "exclude": ["entries.*.request.postData", "entries.*.response.content"] }, "query": { "bool": { "must": [{ "term": { "_entrypoint.id": 5 } }, { "term": { "_api.version.id": 1 } }, { "query_string": { "query": "1111111" } }, { "range": { "entries.entrypoint.startedDateTime": { "gt": "2016-06-01T03:00:00.000Z", "lte": "2016-06-09T13:05:00.000Z" } } }] } }, "sort": [{ "entries.entrypoint.startedDateTime": { "order": "desc" } }] }

any tips?