Macbook Pro 13" 2015: Buy cheaper now or wait?

I'm getting a new Macbook Pro 13 inch 2015 for £900 ($1190) after student discount. That's £100 ($132) cheaper. I'm also getting a Beats Solo2 Wireless as part of Apple's back to school program. I intend to sell that and get around £150 ($200) for that. So the Pro 2015 will cost me £750 ($990).

Now this Beats promotion ends on September 5. So if I wait for the new Macbook launch, I'll only get the 10% student discount, which gets me the new Macbook Pro for £900 ($1190).

My main question is, will I terribly regret not getting the new Macbook by paying £150 extra? It's the same like when they drop the prices of old Macbooks, once the latest version is launched. Is it a mistake to buy the 2015 Pro? Will my Macbook Pro 2015 look completely outdated in a couple of years? I do not want to spend any more than £750 but I need to know if it's a big mistake.

I'll appreciate the forum's opinion.

Thank you!

P.S., It will be my first Macbook ever, so I do not have any knowledge of how they work in the long run etc