15mm isn't actually 1/100 scale. It's closer to 1/107. You would actually need to increase all ranges and movement by about 49% for the scaling to work out. You would also need to increase your play area from the standard 6' x 4' to about 9' x 7.5'. Otherwise your units would cross the board too quickly and mess with the scenario balance.
Base sizes become:
- Small 1.86" x 1.49"
- Medium 2.98" X 1.86"
- Large 3.72" X 2.98"
With that, everything should be proportional and work out to be the same mechanically. If you have a bad back, that table size could be problematic.
I think you may run into cost issues collecting armies at that scale. Plus you'll lose the ability for quick pickup games and tournament play. There are a few new producers of 15mm miniatures such as Plastic Solider Company that have moved to digital sculpting and injection plastic. The detail on these models is much crisper than the hand sculpted models you are used to. You may want to check those out before committing to using 1/72 scale.
If you want to stay at the larger scale, I suggest looking to a game like Bolt Action witch is designed for larger models(in this case 25mm).