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Welcome!What Hardware version is your router? Look at sticker under router.
Link>What
Firmware version is currently loaded? Found on routers web page under status.
What region are you located?
What ISP Service do you have? Cable or DSL?
What ISP Modem do you have? Stand Alone or built in router?
What ISP Modem make and model do you have?
Whats wrong with the 615? If you could give some details maybe we can see if getting the ol girl going with stock FW might help.
Some people have good luck with WRT, some don't. It's kind of advanced and a bit complicated if your not into tech stuff and tinkering. I have the DIR-657, good little router for general home use and some gaming. Doesn't have any cloud features like the 636L does. I haven't had a chance to experience the 636L as of yet. My 856L is arriving soon so that will be my first Cloud router. The DIR-645 is a great router too.
Post back with some details and let see if we can get the 615 going or offer up some suggestions to try.