Ollie's advice is pretty much exactly what I'd suggest. If he's had the device even remotely close to as along as it's been out, even if you do the smaller steps that Ollie outlined, you'll fine better results from a reset if it's a software issue (usually is).
I reset my s4 a couple weeks before I got the Note 4 and it made a world of difference. There have been several updates to the OS since the phone launched and it's really a good idea to do a reset after each upgrade (or at least the "big" ones), to ensure that everything still plays nice together.
I think the "optimizing apps" popup you get when the device first boots up after having installed an update is supposed to help curb some of those issues, but you'll still run into them.
So, in short, there's nothing wrong with trying Ollie's advice, but I'd recommend a factory reset anyway. Doesn't take that long and it'll be on him to set the device back up, but it's nice to get a fresh start with a device, especially, as I said, if it's been around for a while.