So first mobile optimization tip:
Do not use 3D Rigid Body Physics
PlayCanvas includes the 3D physics engine ammo.js integrated into the Editor. Ammo.js is a version of the Bullet C++ physics engine compiled using Emscripten to Javascript. As such it is a relatively large block javascript and a bit of a black box debugging-wise. We have found that Emscripten compiled code will often perform badly on mobile. In addition, 3D physics is a CPU intensive operation and will stress mobile CPUs.
By default a PlayCanvas project will not include ammo in the project. In your project settings there is an option to Enable Physics. If this is enabled, ammo will be included in your project. We will automatically enable this option if you add a collision or rigidbody component to an Entity while in the Editor. For mobile projects, ensure that you have disable physics in your project settings and removed all rigidbody and collision components from Entities in your scenes.
Alternatives
Usually we suggest that you implement as simple a physics/collision system as required for your game. Most mobile games do not need to be simulating rigidbodies and if you can get away with doing simple point-in-sphere or AABB (Axis-Aligned Bounding Box) intersection tests, then you should do that. As noted above, you will achieve must faster results for these specific cases than for a generalized solution like ammo.