BE sure to change the CS pin because the ESP8266 standard CS pin is IO15 which always has to be connected to ground!(in this case change it to 2)
I was wondering about this . Did you make a mistake?GPIO15 pin is not a chip select pin as far as I know . It is the MTDO pin used to boot the chip into a SDIO mode which no-one seems to know much about yet . Its a slave mode for SPI I think though
I think you can use any pin that will go high to act as CS (Chip Select) pin