Teh halia is basically teh tarik with ginger added, which means it tastes warm and slightly spicy and feels like it should be good for you, but the calories are all coming from the same place: condensed milk. Think about it, 35g of condensed milk is barely two and a half tablespoons and it already clocks in at 112 calories. The evaporated milk adds another 28, a bit of extra sugar tips you past 160. For a drink, that is not nothing. To be upfront, these are ballpark estimates because detailed nutritional data on hawker-style teh halia is thin. The actual number at any given mamak depends on how heavy-handed the uncle is with the tin.
The biggest lever you have is how much condensed milk goes in. Ordering kurang manis drops you to roughly 120 calories because you are cutting the condensed milk roughly in half and skipping or reducing the added sugar. That is a 40 calorie saving without giving up the drink. The ginger itself (about 8g fresh) adds almost no calories, so loading up on ginger flavour does not change the maths at all. If you are drinking two or three of these a day at the mamak, you are looking at 320 to 480 calories just from drinks before you even touch your roti canai. Order kurang manis by default and save those calories for actual food.