Numerous collision events (20+ Physics objects, only two of them moving)
This could be an issue, but the numbers don't look very large to me.
High-resolution sprites! 40+ of them! (max is the background 1080p)
This is more a memory issue, probably not related to cpu/gpu heat.
600+ Events (not grouped, all of them in 1 layout/event-sheet) and 30+ global variables
The number of events is unlikely to be an issue, but certain events like long running loops can be. Also limit the number of events that run every tick, and turn pretty much everything you can into triggered events. Updating text every tick can be particularly painful.
Layout size: 15300 x 1480 (however, scroll-to enabled with viewport of 1920x1080/scale outer)
I don't think this would cause any issues.
Other possible factors: Layer Scaling (not constantly), Time-scale set to 1.5, Photon plugin?
Unlikely, but you can test each of these individually pretty easily.
Also how is your game running at 120 fps? Thought it was capped at 60, unless I missed an update somewhere. Maybe your phone is a high fps device as well. I don't recall if there was a way to limit it, but this popped up in a quick search that might be worth trying. construct.net/en/tutorials/limit-framerate-build-fps-1381
Otherwise, its probably mostly up to you to isolate certain things you think may be causing high usage and test and test and test again.