190 mm leca insulates about the same as 45 mm mineral wool or polystyrene. This is roughly equivalent to a modern window (around 1 in U-value). For residential walls, the goal is usually to reduce the U-value to somewhere between 0.1-0.2. Adding approximately 100mm of insulation could be appropriate.
If you have access to insulate from the outside, it's beneficial. Interior insulation in masonry spaces can lead to problematic moisture issues, so you'll need to understand where moisture affects the wall to plan vapor barriers appropriately to prevent condensation. It's possible to insulate internally, as long as you manage both heat and moisture properly.
If it's the house foundation, be careful when digging to the same depth or deeper than the footings, as this can cause settlement.