From: Southern California
Leave them as is. Turn GS off. Don't bother flying the ground support mission until 1942, it is hard coded to be disorganized until then. Instead, use them to fly interdiction. Ground support is quite useless with single digits showing up, it just gets shot to pieces.
In 1942, flip them over to shturmoviks. In the meantime, they can get experience flying interdiction missions. You should save all your tactical bomber production until then. All your pure tactical bomber regiments (you don't have many to start with) should be sent to the national reserve in the meantime, for the same reason, but these regiments with I15bis and I153 have fairly sizable pools so any losses that occur from those interdiction missions won't hurt, and those old airframes do tolerably well flying interdiction.
They can also do straight up direct bombing, although level bombers are better for this, I mostly save the air miles on them for interdiction.
By spring of 42 you should have accumulated enough IL2 production to flip them over.
WitE Alpha Tester