I am getting read to up pot some of my rooted fig cuttings and in need of some advice. I have one, two, five and fifteen gallon pots available. My question is what size pot should I use initially. Should I start small and re pot into a large size later in the season or just repot into a five or fifteen gallon size now? Advice please?

If it's standard plastic pots, then it's usually better to gradually increase size, for example, 1 gallon, then 2 gallon, then 5 gallon, then 10, then 15 or 20. 

The reason for this is because if you put it in a 15 gallon pot right away, there might not be that much roots anywhere except right near the cutting and circling the edge of the pot.  The roots will go straight out from the cutting until they hit something, at which point they will start to circle.  So if you put it into a smaller pot, they'll make smaller circles.  Then when you up pot next time you will trim off those circling roots and there will be more branching the next time. 

I use fabric pots sometimes, and with those there is a chance that a root will try to grow through the fabric and prune itself instead of just circling indefinitely.  So maybe in that case it would be just as good to just go to the large pot right away.  I'm not sure though. The jury is still out. 

I generally go 6 or so inches wider than their current container. That leaves 3" all around for the roots to spread.  If you go from 1 gal to even 3 gal there's hardly any room for more roots.  I also bury as many nodes as I can below the surface so if there's a freeze or rodent damage there are plenty of nodes left to sprout from below the surface.