Book and a Hard Place

One allowance here buys 22,790 EXP, the best on the Lv 15 Alchemist tradecraft rung — matched exactly by 1 other leve of the 6 there, with the rest trailing at 16,920 EXP or less.

Across that rung the return runs from 11,040 EXP to 22,790 EXP per allowance — 4 distinct figures spanning 106%, so the wrong pick leaves 11,750 EXP of the allowance unspent.

On whether to wait: the best Lv 20 Alchemist tradecraft leve returns 21,600 EXP per allowance, 5% less than the best on this rung, while the Lv 10 rung behind tops out at 12,030 EXP.

At Lv 15 this data holds 52 leves paying EXP across 2 categories: the 48 Tradecraft ones average 16,554 EXP per allowance, the 4 Fieldcraft ones 78,432 EXP, which puts this leve 38% above its own category's average.

Engraved Hard Leather Grimoire ×1 is a Lv 20 Alchemist recipe, 3 steps deep through 4 intermediates, costing 10 units of raw material and 9 crystals.

Handing that in returns 2,279 EXP and 47 gil for every unit of raw material the order swallows, and the tree needs Alchemist, Leatherworker and Weaver.