I've scratch built a few planes in the Eaglet's size range and if the RTF weight can be held to about 40 ozs, then a LA .15 will be plenty. Trouble with kit built planes is they are over engineered with the idea that the average builder will tend to over power them. If the kit built plane [Eaglet] is doomed to end up weighing about 48 ozs, then you'll be better off with a .25.
Take a look at Randy Randolph's design called the "Dime" to see a great example of engineering for .15 power. Truth be known, even that plane can go on a slight diet.
Lighter is better, we're talkin' about planes that land at walking speed.