Triac Datasheet/Design Questions
You should pick a triac that is compatible with the optocoupler, not
try to get the optocoupler to work with some random insensitive gate
triac. 

The resistor is to protect the optocoupler (and triac gate) when the
opto is switched on at the peak of the AC cycle. You could see
currents in excess of 1.2A under that condition. The rating on the
data sheet is 1.2A. So, reduce it at your own peril. If you use the recommended value with an insensitive gate triac you will get more electrical noise when 'on' (every half cycle) and the resistor will get hotter.
The maximum current to trigger the triac is 50mA at 25°C Tj but only in the specified three quadrants. You only need to worry about two of those quadrants. The trigger current in Q4 is unspecified and will likely be much higher if it triggers at all (Q4 is MT2-, Gate+). Your application uses only Q1 and Q3. The trigger current can be in excess of 100mA at -40° (see Fig. 2).
The test condition is a gate trigger current of 100mA. The holding current is the current through MT2 when it is on, which is pretty much unrelated to the gate current once it turns on. So the test is you turn the triac on with 100mA gate current, apply holding current through MT2 and remove gate current. If the current is more than 50mA at 25°C Tj it should stay on. If it's colder it might take more current. 


Triacs with relatively high holding and trigger currents (they tend to track) are useful for switching inductive loads and resisting turn-on due to high dv/dt, so it's not all bad.