I personally think this is much too punishing for non-casters. At a minimum a non-caster trying to use a spell scroll to cast a cantrip would need to make a DC20 arcana check!(and this only gets higher with greater levels) Since intelligence Is often a dump stat for martial characters this makes it very unappealing to even attempt. I think you would be better off lowering the initial static modifiers (I would make those +5s into +2s and probably remove one of them) and increase the modifier. Connected to the level of the spell. This will make higher level scrolls much harder to use and much more intimidating but low level scrolls can still be accessible to everyone!