the Epson WF7515 printer uses only color inks (yellow, magenta, cyan) when printing on photo paper. The reason is that black ink is not scratch resistant on glossy or satin paper - this applies to all Epson printers with "Durabrite" pigment inks.
2) not being able to print at all:
Please check your USB or WLAN connection to the printer.
Can you print with the original Epson printer driver?