In the 1860 census, 20% to 49% of Southern families owned slaves. The only two states below that were Maryland and Missouri at 12% and 13% respectively.
The latter part of your statement is completely lacking in logic. If you’d like to forget everyone who couldn’t own property you might as well write off the slaves themselves as well — since they comprised from 20% to 57% of the population we can now claim 0.75% to 1% owned slaves! Except we are using different rules for each side of an equation, which makes any claims resulting from it worthless — such as your original 1.5% claim.