Please support for D-link DIR 615 REV. P1
It's all up to you: https://openwrt.org/docs/guide-developer/hw.hacking.first.steps
Device support doesn't materialize out of thin air, it always needs someone with the hardware on their desk to work on it. So far you're the only one who has access to this device and is interested in it, which means the task would be yours to take.
Given that there doesn't seem to be any hardware information about it (and a wide variety of vastly different devices sold under this model name), it's not even clear that it could be supported in the first place. Many hardware revisions of them sport completely insufficient hardware specifications though.