Can I use a spare tire from a 2010?

It should work as a spare. Strapping it to the trunk is the hard part. Some folks here said its impossible because it wasnt shape to take a donut.

 

You should still have a spare tire punch out under the foam below the trunk. You can buy the foam inserts that come with gen4 with a spare or use a jigsaw and carve out space for it in the foam you have. Did you keep the screw in bracket from your old spare tire? It'll still fit in that hole, at least the parts from my 2013 fit in my 2016

Your old spare may be getting old. Make sure the tire itself can hold air and doesn't have any cracks.

 

It'll work. The 3rd gen spare size is actually closer in OD (Outside Diameter) to the stock 198/65R15 tire size than 4th gen; not sure why they changed. It's at most 1/8" less in OD.

You can check the OD variation for yourself, by stacking the temp spare atop a regular wheel/tire, on a slab. Align the outside faces with a carpenter's square on one side, then go 'round the other side and again press the carpenter square up against the tires, to see the variation.