Blender's slow, is this my hardware???

Hello People,i Have a :
I5 2500
16gb ram
1tb disk
Nfida gforce gtx 960 2gb gpu.

Now when i’m middeling a tree. I can only Make one tree.
And then i get the error:

Out of Memory.

I discover that if i go a little bit too far, blender is going very slow.

Is this my hardware?

I already put on the open gl to graphic Card.

What is it, on YouTube all the middeling Goes very smooth.

Whiley pc is very slow.

And when i want to upgrade.

In what hardware should i think.

(Sorry for my bad english)