While I'm inclined to say wait and see what is to come, I really don't have any guilt about suggesting buying a 2015 rMBP.
I recently picked up a 2015 rMBP 15" base model (2.2GHz, 16GB RAM, Iris Pro) and couldn't be happier (to be fair, I've been working on an 11" MBA for a while...)
Considering the circumstances of how "old" the current-gen MBPs are, the deals can be pretty good for new; and also Apple Refurbished is always a great deal.
I'm also of the belief that one should generally wait for at least the second generation of a "new" or "redesigned" product from any company--whether it's cars, guitars, or computers... Sure, Apple has most things down, but there seems to almost always be some sort of bug to be ironed out during the general manufacturing process--sometimes they just need the time to figure out how to make the product en masse.
I'm not saying one should always be "cautious" or "paranoid" of first generation products, but it's been my experience through life that if I'm going to spend a significant amount of my money on a product, I like to be sure.
That said, you can always check out the rumor mills, and Apple news sites and see what their bloggers are saying and claiming to know about the future of the MBP--from there you can judge and compare what we think will happen to what we know is available in the 2015 lineup and ask yourself "is the rumor that....________________ worth waiting for, or should I buy now knowing that the 2015 (or older..) model will suit my needs..?"
As an example, I had to decide in 2016 if buying the 2015 rMBP 15" was worth it for me.. Considering it's running an i7 from 2013, I had to ask if the raw power of that processor was worth my investment or was it more important for me to invest my patience in waiting for Apple to introduce something presumably more flashy and "powerful." In the end I looked at the stats, and numbers and said the 2015 was good enough for my needs. Which is the key: consider your needs; gather the information available, and then you can make a truly informed decision. There's really no amount of typing we can do on this support group to make a decision for you.
Good luck.
-Scott