Let's be helpful - very good idea. Seems to be not that easy though...

To throw in my 2 Eurocents, I think the general concept is a given and requested is only information helpful to put it into practice. Shoe showed on the back side of an envelope that it can be done, so we think about how it can be done.

Climbing to 15k ft and cruising there is possible with an airframe as already suggested. For me the discussion showed that a narrow (high aspect ratio) wing is most important, but not planform or streamlining. Airfoil may play a role. The airframe's overall design determines how good it climbs and at what speed.

Now the electric drive has to match it to get the high efficiency required (65%) at that speed. It has been said here several times that an as big as possible propeller should be used. That's far more important than pull/push or other design features.

There are some well-designed (basically efficient) carbon folding props, just the suitable diameter and pitch has to be found out. High efficiency at low speed requires a slow-turning prop and drive. There are some low-kv outrunners, but maybe a more conservative outrunner or even inrunner with a gear would be better. (Gear has been mentioned before as well.) There are ready-made outrunner/gear combinations (e.g. AXI).

Attached pictures show characteristics of an F3A drive by AXI. They go to show that the prop determines the drive's overall efficiency (prop, gear, motor, ESC, battery, cables, connectors). And that efficiency has a marked maximum at some speed (the light blue line in the second diagram). In this case, though, the required 65% are achieved between 27 and 46 m/s. That should be too fast for this project but that just means one has to choose/layout the drive differently. (That can't be done on the back side of an envelope, but it's not that hard, either.)

Another small but maybe important aspect comes to mind. Climb and cruise are quite different modes for the drive. To get better efficiency in both modes full-size airplanes have variable-pitch propellers. There is even an automatic variable-pitch hub for model folding propellers, as presented in the glider forum a while ago ([link=http://www.rcuniverse.com/forum/m_10815942/tm.htm]here[/link]). Might help a bit. (Dang. Seems to be no longer available.)

Last picture a typical pusher configuration, for aerial pictures in this case.