[url]http://www.plantithawaii.com/[/url]

They say:

[quote]Lychee is quite adaptable in its soil requirements but prefers a moist rocky soil. It needs high humidity and abundant rainfall. You can see beautiful fruiting specimens from about sea level in the Hilo area up to about 1,000 feet.[/quote]

Now that tells me that it probably won't fruit or fruit well at 1500 ft.

"Longans are usually eaten fresh but are also dried and canned. It is a delicious, juicy fruit with a very sweet and pleasant musky flavor.

It is a large spreading tree, which bears many clusters of golden-brown- skinned fruit at the ends of the branches. The juicy white fruit is about the same size as the lychee with one black shiny seed.

It does well in most areas of Hawaii below 2,000 feet if provided with abundant water."

http://www.ctahr.hawaii.edu/oc/freepubs/pdf/F_N-2.pdf

http://www.ctahr.hawaii.edu/oc/freepubs/pdf/HC-1.pdf