F-15C trim is useless atm, it's too rough. Trim is used to add a fine level of control for comfort and not as a backup stick in case it fails. They need to make it more sensitive, until then it's just flat out worthless. I'm unsure why it hasn't been done already, can't think of anything that could make this otherwise simple fix difficult. But I'm no ED employee :D
It's like your plane rolls left due to weight imbalance, you try to trim and then *woosh* now it rolls to the right, much harder. What a troll system!