In addition to this, in my case (and depending on device types) the SNMP Max repeaters made a huge difference - if you have long polling on some devices - can see it all under all devices: /devices/format=graph_poller_perf/from=-24hour/to=now/
See my SNMP max repeaters results on this post and the one after it: Debugging graph spikes from high latency links - #6 by rhinoau
Fiddling modules on and off never made much different to my poller timings.