It will make no difference in the heat loss if you switch to a tankless water heater if the location is the same. The heat loss from the water heater to your fixtures has nothing to do with the source of heat.
However, for energy savings it is always smart to use a tankless water heater. The advantage is not having to store the water before you use it. If you do not want to take on the cost of a tankless water heater, you can purchase an insulating blanket for your water heater to slow the heat loss.