According to badwiki, evokable invis is a flat 250 hunger. Your 29 casts add up to 1.2 rations; a noticible amount, but not a lot.
Your banishments are actually more expensive, at 300 satiation, and again 29 casts. That's 1.6 rations.
Corrupt costs 750 hunger, so those 4 casts is another 0.6 rations.
Currently Deflect Missles (or the invis spell when you find it) costs you 225, or slightly less than your evokable invis.
Just for comparison with on of my SpEn:
- Code:
Action | 1- 3 | 4- 6 | 7- 9 | 10-12 | 13-15 | 16-18 || total
-------------------------+-------+-------+-------+-------+-------+-------++-------
Melee: Dagger | 56 | 87 | 158 | 681 | 1450 | 245 || 2677
Fire: Blowgun | | 11 | 23 | | | || 34
Hunting sling | | | | 5 | | || 5
Throw: Stone | 5 | 3 | 6 | 6 | 11 | || 31
Cast: Corona | 3 | | 1 | | | || 4
Ensorcelled Hiber | 9 | 18 | 32 | 84 | 102 | 1 || 246
Confuse | | 1 | 7 | 97 | 156 | 3 || 264
Tukima's Dance | | | | 16 | 16 | 2 || 34
Dazzling Spray | | | | 12 | 39 | || 51
Regeneration | | | | | 8 | || 8
Invisibility | | | | | 4 | 4 || 8
Invok: Call Merchant | | | | 2 | 4 | 1 || 7
Evoke: Wand | | | | | 5 | || 5
Use: Scroll | 1 | 6 | 6 | 12 | 29 | 1 || 55
Potion | | | 7 | 3 | 11 | 1 || 22
Stab: Sleeping | 18 | 29 | 30 | 105 | 244 | 16 || 442
Distracted | 1 | | 1 | 13 | 50 | 11 || 76
Confused | | 1 | 8 | 37 | 66 | 2 || 114
Invisible | | | | 2 | 28 | 23 || 53
Fleeing | | | | | 1 | || 1
Eat: Pizza | | 1 | | | | || 1
Fruit | | | 2 | | 2 | || 4
Bread ration | | | 1 | 1 | 4 | || 6
You're using WAY more food then I am. My supposition is that hitting things to death with a dagger is punished fairly heavily by the food clock. And it's not your regen amulet; that increases food usage by 2 per turn you're below full health, but means you spend less than half the time resting.
Edit: Since this is GDD and not CIP... I would suggest we remove the ability of spriggans to hit things with a shortblade when it isn't a stab, to prevent people from starving due to leaning on tab.
Edit2: The food consumptions at Level 15 are:
That's a difference of ~9 bread rations. Way more than your skill usage can account for.