Yes, a lipo of even the same mah rating will run longer than a nimh. Reason is the lipo converts very little energy into heat, unlike the nimh. The difference depends on how hard you are discharging and thus heating the nimh, but 20 to 30% improvement is not uncommon.

Also the lipo handled correctly will be more stable over time. Both in runtime and performance (actual voltage under load, not the common 7.2/7.4 nominal voltage rating). Depends some on the nimh, they vary from brand/cell type to another. I suppose the same is true of lipo, but since they are much more stable to begin with the differences from lipo to lipo seem to be smaller.

Combine a good lipo like you mention with a say 17.5 or 13.5 brushless motor and you will probably get 30 to 40 minutes of run time. As a fellow old timer this stuff is sweet indeed.