Hi Andrew,
Some drivers specsheets have the displacement, others don't.
In this case if you consider 4L you will be fine, as a standard (15 inch - 4.0 liters). Look at the parameters of displacement for similar drivers,
Speaker Detail | Eminence Speaker
Also WinISD (free software) has a last page menu for that calculation, when you insert the driver measurements into the application.
If you want, give a look at on-line calc. (Speaker Driver Displacement Calculator) here.
JBL GTO 1514 specs
If it is for a car system you can use the recommended enclosure,
if for home use 150-160L, 150L = ~5.3ft³. You probably want to use the least volume size cabinet you can do with EQ, what (net) are you planning for your project?!