It kind of depends on how fast you body neutralizes the acid group on the lantus molecule and makes it soluble. Althought the pH of the blood is very carefully controlled Iam not sure that tummy grease is.
More important, if you inject a small amunt it would not last as long as a larger amount because of the geometry of the problem. A small amount will have a larger surface to volume ratio than a large amount like a drop of water on a hot stove the smaller the faster gone. Another analogy is that a smaller droplet of water falling in dry air will evaporate faster that the larger one.