What can cause my 2015 Malibu trunk fuse to keep blowing?

The trigger wire from the cab to the latch has a bare wire touching grounds,then it blows the fuse.Or the latch solenoid is shorting out then the fuse blows.Tape up bare wires and or replace the shorted latch solenoid.The light for the trunk may also be shorting to ground.Any bare wire to metal should be taped with electrical tape.

The power supply wire is shorting out somewhere between the battery and the bulb and will be difficult to find.  Pull the fuse for the light and don't worry about it.  It is not worth the effort to track down.

A SHORT! 

Or the fuse value may be lower than its supposed to be. Don't put a fuse in that has a higher value than it's supposed to be.

A wire has insulation off and is touching sheet metal, or maybe the solenoid or light itself has a problem. You didnt say if it was the trunk opening solenoid or the trunk light.  They used little metal clips to hold the wire to the inside of the trunk.  Maybe at one of those clips the insulation got sliced through. 

If not, follow the wire and check it.  Sometimes the harness is under the mat on the trunk floor and something that you put in the trunk damaged it. 

Maybe the switch has a problem. 

My last idea is body metal that got bent from an accident sometimes cuts into wiring.  Was the car hit?

You have a short somewhere in the circuit. Could be frayed insulation causing two wires to touch, a faulty latch or push button, you have to start at one end of the circuit and work toward the other end.

Try disconnecting the electric trunk latch connector if you can open the trunk with a key. If the fuse doesn't blow the problem may be in the electric trunk latch assembly. If the fuse still blows inspect the wiring in the area of the trunk hinges for a short.

The wires leading to the trunk light got pinched somewhere and are shorting out and blowing the fuse when you open/close it. Has nothing to do with the contents.

If you mean the trunk light fuse, the bulb assembly or wiring is shorting.  Disconnect the connector and check if fuse still blows.  If it does not, replace bulb assembly .  If it still does, there is a wiring short.  Look for burn marks in the wiring to the bulb.  You might need the help of a mechanic for a fix.