Iphone 4S with 4GB of "other" data? Since ios 9 was released?

My 4S with 8GB has 4GB occupied of "other" data (I believe it's since ios 9 came out, before that it had 2,5GB which I believe it's normal)

I already restored it to factory settings. It was ok in the beginning but after 1 hour it was already 2,5GB and now it's 4GB. (I only downloaded the apps)

It has no ios 9 update download on the storage.

My current ios is 7.1.1

It's ridiculous that 8GB it's not too much, and I only have 2GB to use, once 4GB are occupied with something I don't know, and it seems that nobody does.