The 15" I think would be good cause of the larger screen and performance....but I'm not too sure I actually need the performance or bigger screen cause I have a monitor and my current 13" handles my tasks fine.
The thing with "need" is that you don't even "need" what you currently have. You could do everything you mention with a 2010 MacBook.
So any choice you make isn't based on need. It's based on benefit, value, and wants. The faster 15" is a benefit. The larger screen is definitely a benefit, and sounds like a want. The smaller size of the 13" is a benefit, doesn't sound like a want.
Of those, it sounds like the 15" is the right choice for you right now.
But that leaves value. If you can afford it, you
probably should go with your wants (assuming you can really afford it and not simply can pay for it--that's where needs become more important, as if you can't really afford it, you shouldn't exceed your needs, though that means sticking with what you currently have!).
All of this you already know, which is why the decision is so hard. And that boils down to:
If you pick the one you want, it might be too big. If you pick the one you are familiar with, you might have preferred the larger one. It sounds like price really isn't an issue, but a hopeful excuse.
So with that all said, I'd recommend the 15". If for no other reason than that once you've owned it for a while, you'll
KNOW FOR CERTAIN instead of just wondering (which will nag at you indefinitely).
The bonus points here are that if the screen is as nice as you are hoping, you can possibly sell your monitor to help pay for it (tidying up your workspace in the process) and if you don't like it, you have 14 days to return it with zero financial loss.
Also, the performance difference is noticeable. You don't need it, but you will enjoy it (but only if you can afford it).
If you've read this far, your gut should know the answer. If the 15" sounds good, go for it, it's the one you want. If I sound like I'm full of ****, then I think your gut knows you really do want the 13".
Good luck!
(and one last thing, to help ease your mind, no matter which you pick, you'll be happier than you are now, so don't sweat it too much, even a mild mistake in choosing the "wrong" one is not going to be a bad outcome)