Hello and welcome to you and sweet Tigger. Can you give us a little background on Tigger? Any other issues when he was diagnosed? Just asking because if he's showing ketones, you want to avoid skipping shots. Oh, and here is your
previous post on the Feline Health forum for those wanting some background.
Good job getting doing home testing now, and getting the spreadsheet going. Lots of good information in the Remarks section too.

Take a read of the yellow starred Sticky Notes on this forum. We have a choice of two methods for dosing, Tight Regulation protocol and Start Low Go Slow. See which one suits you best. For both of these dosing methods, we would do dose increases by 0.25 units at a point where Tigger is now. But now that you've gone to 1.5 units, stick with it for a while. You'll need to hold the same dose for at least 6 cycles for the depot to build again after the skip. We also shoot the same amount AM and PM, unless they earn a dose reduction.
Eventually you'll be able to shoot lower numbers once you've got more data on how Tigger responds to insulin. A cat's insulin cycle tends to be flatter when they start lower. Lantus is great at keeping lower numbers flat.