T56A-7 and -15 engine nacelles are identical. The defining difference between a -7 and -15 engine is that a -15 has hollowed out 3rd & 4th stage compressor blades. This allows for a higher operating TIT (turbine inlet temperature) resulting in greater torque available to the prop.
There are other subtle differences (not visible outside the nacelle) in things like the synchrophaser, TD system, oil cooler system, generators, hydraulic pumps, etc., but those are more aircraft specific rather than engine specific (H1s vs. H2s or H3s). Some older aircraft equipped with -15s (e.g., old H models and \"bionic Es\" ) have the same engine associated components as those aircraft equipped with the -7 (the good old E model).
Be well,
John \"The Manatee\" Haverstock
