We'll understand if you buy the iPhone 6 between now and September. That said, if you can wait, you should probably wait a few more weeks just to see what Apple has up its sleeve for 2015. From the look of it, the iPhone 6s should be a very solid addition to the iPhone family.
The iPhone 6 is still an excellent phone but the iPhone 6s should be a better one. Rumors suggest that it will have a 4.7-inch display with Force Touch technology, huge camera upgrades, a similar design, a new processor that could improve battery life, and more.
The iPhone 6s launch isn't expected in August but it is expected in September. Maybe even early September like last year's iPhone 6 launch. Point is, we're probably only a few weeks away from a spectacle that happens just once per year.
It's probably in your best interest to wait if you can manage.