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.

I agree. Small trainers, built reasonably light, are just great. Kits gave small planes a bad name because they were over built and came out heavy if you weren't careful in the construction. Most have disappeared.

I loved my TF Schoolmaster, LW Champ and my Sig Kadet Jr. The latter was comparable to the Eaglet and flew great with a plain bearing .25. The LW Champ was bigger, yet flew beautifully with a plain bearing .15. It weighed 45 oz and had 4 square feet of wing. I found no disadvantage compared to larger trainers at all. Why feed a big engine when you're learning the basics?

Yeah, the 'Dime' looks ideal.

Jim