Okay a normal DC is calculated like this.
10 + the spell level + your primary stat bonus. Int for Wizards, Chr for sorc and Wis for Druid and Cleric.
+ your spell focus for the school of magic if you have those feats.
Spell focus +2
Greater spell focus +4
Epic spell focus +6
using the chain lightning example.
Chain Lightning is a 6th level spell.
to see what it is capable of I'm going to assume your 40th level with a 40 prime stat. Just for ease of calculations.
The DC will be 31 (10 + 6 + 15 = 31). this can be raised by taking the feats spell focus, greater and epic, by +6, to a 37. (with this the lizard women only has a 50/50 chance of saving)
Normal damage: 30 - 180 average of 90 save for 45.
Maximised: 180 save for half is 90.
Empowered: 45 - 270 average of 135 save for 70.
A lizard Women Sorcereress is a spell caster they are going to have high saves versus spells. Lizardmen in general are agile and have good reflex saves. Not to mention she is considered a boss type creature. She is also a 25th level creature with an unadjusted CR of 40, meaning you should need to be 40th level with standard gear to take her down in a one on one fight.
I would rather not make a change to the basic engine such as basing the DC off of your level. this would have several effects to game balance.
1. NPCs can be 60th level, ohh you will never make your save against them.
2. This will make it harder for spell casting classes to multiclass if they want a nice DC for their spells.
As it is now you can maximise your DCs, for one school of magic, by about 24th level probably 21st really. Excluding your prime stat bonus. So that way it is now makes caster classes more flexible with multiclassing.
If I need to adjust the saves of some creature that I can do.