V2.15 is a version number, but does not say which firmware it is. Googling I find often refernces to longer but also marlin firmwares. So it might be modified marlin where they have own version numbers. Just for comparison here a marlin 2.1 response on M115
Send:9:40:24.279: N4 M115 ; Get firmware capabilities and info
Recv:9:40:24.295: FIRMWARE_NAME:Marlin 2.1.2 (knutwurst, Github) (Dec 26 2022 14:39:39) SOURCE_CODE_URL:github.com/knutwurst/Marlin-2-0-x-Anycubic-i3-MEGA-S PROTOCOL_VERSION:1.0 MACHINE_TYPE:Knutwurst's Anycubic Printer EXTRUDER_COUNT:1 UUID:b6153152-86fb-4cd8-bda7-91c6a04c467d
Recv:9:40:24.295: Cap:SERIAL_XON_XOFF:0
Recv:9:40:24.296: Cap:BINARY_FILE_TRANSFER:0
Recv:9:40:24.297: Cap:EEPROM:1
Recv:9:40:24.297: Cap:VOLUMETRIC:1
Recv:9:40:24.297: Cap:AUTOREPORT_POS:0
Recv:9:40:24.298: Cap:AUTOREPORT_TEMP:1
Recv:9:40:24.299: Cap:PROGRESS:0
Recv:9:40:24.300: Cap:PRINT_JOB:1
Recv:9:40:24.300: Cap:AUTOLEVEL:0
Recv:9:40:24.300: Cap:RUNOUT:0
Recv:9:40:24.303: Cap:Z_PROBE:0
Recv:9:40:24.303: Cap:LEVELING_DATA:1
Recv:9:40:24.303: Cap:BUILD_PERCENT:0
Recv:9:40:24.304: Cap:SOFTWARE_POWER:0
Recv:9:40:24.304: Cap:TOGGLE_LIGHTS:0
Recv:9:40:24.305: Cap:CASE_LIGHT_BRIGHTNESS:0
Recv:9:40:24.307: Cap:EMERGENCY_PARSER:1
Recv:9:40:24.308: Cap:HOST_ACTION_COMMANDS:1
Recv:9:40:24.308: Cap:PROMPT_SUPPORT:1
Send:9:40:24.308: M876 P1
Recv:9:40:24.309: Cap:SDCARD:1
Recv:9:40:24.309: Cap:MULTI_VOLUME:0
Recv:9:40:24.310: Cap:REPEAT:1
Recv:9:40:24.310: Cap:SD_WRITE:1
Recv:9:40:24.312: Cap:AUTOREPORT_SD_STATUS:0
Recv:9:40:24.312: Cap:LONG_FILENAME:0
Recv:9:40:24.313: Cap:LFN_WRITE:0
Recv:9:40:24.315: Cap:CUSTOM_FIRMWARE_UPLOAD:0
Recv:9:40:24.315: Cap:EXTENDED_M20:0
Recv:9:40:24.318: Cap:THERMAL_PROTECTION:1
Recv:9:40:24.318: Cap:MOTION_MODES:0
Recv:9:40:24.318: Cap:ARCS:1
Recv:9:40:24.318: Cap:BABYSTEPPING:1
Recv:9:40:24.320: Cap:CHAMBER_TEMPERATURE:0
Recv:9:40:24.321: Cap:COOLER_TEMPERATURE:0
Recv:9:40:24.321: Cap:MEATPACK:1
Recv:9:40:24.321: Cap:CONFIG_EXPORT:0
Also the age of 2018 indicates in could be marlin 1.x version but even marlin 1.x behaves different.
Is Pronterface working correctly when you print a file with that?