There is nothing wrong with 6.1.7, it's fully supported by Synology and will be for some time.  I'm sure you understand you cannot upgrade the DSM to 6.2 without using 1.03b loader. That said, I can't see any reason you cannot use 1.03b and DS3615 as your chipset NIC (Q77 Intel 82579LM/82579V Gigabit Ethernet) is supported by e1000e which is what is required.     I actually have one of these in my office that I was making ready to sell... I might try to do an install on it