Assuming you have the 1 1/2 HP Optiflo pump, flow rate on typical AG plumbing is 50 GPM on high which means it would be about 25 GPM on low speed. So marginal. But a heater's operation is dictated not on flow rate but on pressure. If the pressure is too low, the heater will not kick on but because you have an AG pool, the pressure should be fine on low speed.

If you want more than guess, I would need a picture of your equipment setup and also the filter pressure on high speed.