Personally I have found the S3, to S4, to S5, to S6 and S7 was a definitive advantage each time, in terms of performance.
In saying that I gave my S7 to the wife and currently use an S4 ... plus I have a spare.
It does the job.
The S5 is slightly better ... it is a good fone.
I suggest taking it to a fone shop and putting a new glass cover on the screen and a decent cover, and pocketing your money for something else.
The S5 and S4 do everything the new fones do ... why bother?
You can also clear the cache and remove all of your pictures and other stuff cluttering up the fone onto external storage ... thus speeding it up a bit.