Skydiving operations pilot reported going through assigned altitude and not wanting to change the center of gravity for the jumpers; started a slow descent to assigned altitude.

Narrative

I was performing parachute operations under part 91 in a C90A. I was operating under VFR in class G and E airspace with sky clear and no clouds. Upon climbout and circling the airport preparing for skydiving operations. ZZZ Approach advised that there was traffic at 16;500 feet and was moving in opposite direction 3-4 miles; I cannot remember the direction ATC gave at the time. As I approached 15;000 with requested altitude for skydiving operations and started to level off to make a jump run. The light was activated for the skydivers to open the door to spot their dropzone. At that time; I was focusing on all the skydivers moving to the rear of the aircraft. My CG shifted to the rear with the skydivers moving to the rear of the aircraft and started to climb. When looking back at my flight instruments; I noticed that I was approaching 16;000 feet. With the skydivers at the rear of the aircraft and not seatbelted in due to getting ready to jump from the plane to skydive. I did not feel it would be safe to firmly push forward on the yoke to immediately begin a decent back down to 15;000 feet; again due to the fact that the skydivers were not seatbelted and would be in danger of injuring themselves if I firmly pushed forward on the yoke creating negative G's and potentially injuring the skydivers. I leveled off at 16;000 feet and slowly started to descend back down to 15;000 while the skydivers were jumping from the aircraft. At that time; that is when ATC contacted me and stated possible pilot deviation and gave me a number to call. After landing safely; I proceeded to call ZZZ approach from the number they provided