The following database is gathering the stock firmware for BQ devices. Check out if the flash for BQ BQS-5515 Wide is available. All files contain BQ official stock firmware. You can download Android software for BQ BQS-5515 Wide completely free. Use the following flash to update, downgrade or simply flash your device.
In order to flash your BQ BQS-5515 Wide you need to check out either your device is using MTK (the firmware name should contain "MT") or Qualcomm chipset(the firmware name should contain "MSM"). In the case of MTK, you need to use the SP Flash tool to flash the software.