Question about the subscription

[Sheer]

So I was wondering if I were to buy a ps4 copy of the game does my $15 sub allow me to play both at the same time? Like play on the ps4, then go to my pc if need, or vice versa.

As long as you have a copy on both your PS4 and your PC, you're set. The subscription is bound to your account; the one-time purchase is bound to your system.

Edit: Just to be completely clear, you can't play on your account on two systems at once. So you can only be logged into your PS4 or your PC, not both simultaneously.