Just run away from normal fights, these you can't run from(boss fights for example) won't level you up to 10. If it is still "to hard", just let Crono die all the time so he won't gain any exp, because the level of the first member of your party determines Spekkio's form(and this is Crono most of the time).
His first form only targets single enemys with his magic, so just have some revives ready, otherwise the fight is a joke.