Setting a large number of particles to a large size will perform poorly on mobile devices that have a low fill rate (number of pixels it can draw per second). 

Due to the way AGK draws particles there is a platform imposed limit on the size of particles that varies from device to device. If you exceed this limit then the AGK will fall back to drawing particles as normal sprites that will draw more slowly. For this reason it is recommended that you keep particles to a size that means they do not take up more than 64 pixels of space on the device screen.

TAgkParticleEmitter Properties