That seems improbable, because LLC owners usually recognize all of their income as pass-through distributions; this would be akin to a capped 15% tax on all wealthy people.

The reason you can propose drastically cutting the corporate tax is that it's a tax on money that is again taxed as income when it reaches households. The whole point of an LLC is not to do that.

LLCs that retain lots of income in the corporation indefinitely can elect corporate taxation, to which the proposed reduced rate would presumably apply. But when the LLC distributes that money back to its members, it is again taxed as income. In any case, that may be the basis for this proposal applying to LLCs.