The 1.5SMCJ9.0AS_R1_00001: That 15.4 V ceiling is what the downstream circuitry sees during a transient event, so the protected rail needs to survive that clamping level without damage. The reverse standoff of 9 V defines the normal working voltage — the TVS stays reverse-biased and invisible on the rail until a transient pushes it into avalanche breakdown. The 10 V minimum breakdown voltage gives headroom above the 9 V standoff, so it does not turn on during normal 5 V or 12 V rail operation.
Temperature grade and DO-214AB package
Junction temperature, not ambient, is the limit; the PCB copper and thermal pad under the SMC body set the actual thermal path.