Based on community feedback, try: (universal, WebUI 11.1.1.1) Works on most hardware revisions (including s-22).
Before flashing, you must ensure you are downloading the correct firmware version. Installing the wrong software can permanently brick your device. Technical Specifications Huawei 4G LTE CPE Router Model: B315s-22 Firmware Type: Universal / Global / De-branded huawei b315s-22 universal firmware download
If the web interface does not have a local update option, you must force the firmware using the Huawei Multicast Upgrade Tool: Based on community feedback, try: (universal, WebUI 11