Step 1: PMFBY fixes three flat farmer-premium slabs by season and crop type, rather than charging the full actuarial premium to the farmer.
Step 2: Kharif food and oilseed crops sit at the 2 percent slab, and commercial and horticultural crops sit at the higher 5 percent slab, leaving the Rabi food and oilseed crop slab as the lowest of the three.
Step 3: That lowest, Rabi-season slab is fixed at 1.5 percent of the sum insured. \[\boxed{1.5\%}\]