Power dissipation in triac driver optocoupler
Then that is fine. The resistor only conducts for a short period of time at start of each AC half cycle when the phototriac is on. And only until there is enough current flowing through it to turn on the main triac. The number determining the dissipation is the turn on current at the triac gate and as it is working fine this is low enough not to cause dissipation problems for the resistor.