Hi Susan
Do you really want to know the answer?
Fish and Chips from a chip shop (chippy chips):
Regular Chips (227g):
17½ Syns
Large Chips (340g):
26 Syns
Battered Fish, Small (120g):
10 Syns
Battered Fish, Average (180g):
15 Syns
Battered Fish, Large (225g):
19 Syns
From what you describe I would guess about 20 Syns