Most floor tile is between 1/2 and 3/4 inch thick. That is thin enough to require a solid base. You should keep some tiles in reserve just in case heavy cookware or a small appliance is dropped and cracks one or more tiles in your kitchen floor. You may not be able to find the same tile later on.

I'm not saying they won't work outside, but they will be less likely to break when placed on a solid, compacted base. Decomposed granite or some other rock dust would be my preference. Sand might work, but it might attract ants that could undermine the tile, or it could be washed out during even minor flooding.

Lay the tile on the ground where you want it. Check out the stride between tiles by walking NEXT to where you have laid them. Do not walk on them until they have a solid backing. Once their placement is set, use a spade to cut around them. Set the tiles aside and dig up the mulch and soil to a depth of 2 inches. Fill the hole with the base material and tamp it down. Then lay the tiles atop the leveled, compacted base and fill in around them with mulch.

Do yet get frost? Do you get rain? If so I would not use indoor tile outside.

Too slippery in the rain. Maybe use them under large pots as a base