We (my wife and I) have beaten it on Core difficulty, though it took three or four goes and I think our party was one or two levels higher than yours.
Some advice:
- you have to gang up on them. They regenerate scarily quickly, and do a lot of damage, and most disastrously, their attacks lower your fire resistance, so you've got to arrange things so most of you are attacking one or two while the rest are being held off somehow.
- possible ways of holding them off: they're fairly ineffective at killing Mordenkainen's Swords. (They will eventually, because they'll lower their fire resistance and then torch them, but it takes a while. Their physical attacks can't do much to someone protected from magic weapons - I had a fighter/mage, which you don't, but a boosted Aerie could at least hold them off.
- You need to start the battle as protected from fire as you can possibly manage - get everyone up to 125%+ fire resistance. It's true that they'll break through it eventually, but it takes time.
- look for ways to protect people from their fire attacks other than fire resistance. For instance, fireball doesn't penetrate Minor Globe of Invulnerability; magic resistance protects you from pretty much everything. Neither of those defences can be brought down by the giants.
- Slow is effective both at reducing their mobility and at halving their regeneration rate. Use several to be sure, possibly combined with Malison.
- The giants don't have any magic resistance other than their fire resistance. Horrid Wilting works particularly well on them.
- use sequencers, spell triggers and chain contingencies to hit them hard right at the start. You're not quite high enough level for a chain contingency, which is a shame - we had a CC containing three Mordenkainen's Swords, spell triggers containing two slows and a Malison, that sort of thing.
- it should go without saying, but make sure you're absolutely as protected as you can manage with pre-battle spells before you go in. A rough rule of thumb by TOB is: if there's still room on your character's portrait for more icons, you haven't cast enough pre-battle magic.
If you do want to uninstall, incidentally, I'm reasonably certain it won't have any serious effect on your install.