Phone memory problem

[AnandSRM]

when the phone memory is occupied to about 1 gb, the phone starts to lag abnormally (despite the internal memory has a free space of 3gb).I have done factory reset twice.Phone is non-rooted.Disabled Google plus, chrome, Google books, Google movies.

[Johan]

Are you sure that its related to storage?

Use the recent app's to check what's running in the background when you experience this and close some app's.

[AnandSRM]

Whenever this happens, I always check the recent apps.It's not helping.I'm using greenify too.
Are you suggesting me that low phone memory has nothing to do with this?please suggest me on this issue.