windows 10 - Game is very slow to load when computer is starting

One of a game I play (Overwatch, not to mention it) is very slow to load when the computer, using windows 10 x64, has been started for less than [at least] 5 to 10 minutes. VRAM usage is really low and all animations and 3D models in the game take ages to load (when they do, VRAM usage is back to normal).

What may be the cause of it ?

I just changed my graphics card to a GTX1080, so my VRAM is most certainly OK (the problem was here before, too), can my RAM be so old that it becomes unresponsive/slow when it has not "warmed up" ? (it's 2 years old) Can it be tested ?

It may also be windows that slows the computer down with random services at boot, how can I know if it is the case ?

other non-3D applications are not slowed down.

Thanks

Answer

What else is windows doing at the time?

When windows has "started" it's still loading all sorts of background services and load on startup applications.
Microsoft know that people don't normally notice how long it takes their computer to finish starting up. What they notice is how long it takes the desktop to appear. So they put a lot of effort into making windows put the desktop up and respond to mouse clicks as soon as possible rather than waiting until everything has finished loading.
And even once things have finished loading there will be a half dozen different things checking if there are updates to download and apply and various other housekeeping tasks that take place every now and then in the background.

You will probably find your game is going full speed sooner if you wait a couple of minutes before starting it. Give the computer a few less things to constantly switch between and things will normally get done a little quicker.

The RAM doesn't slow down with age or need to warm up, the computer runs it at a fixed clock speed based on how fast the BIOS has been set to run it. If it doesn't run at that speed then the wrong value is read and data gets corrupted. When that happens to any extent the computer will normally lock up or blue screen.
Electronics actually run faster when cold so warming up is more likely to cause a crash than have any speed impact.