This problem comes up A LOT. This speed problem is a daily occurrence. Often the result of not enough research and a development practice not set up for mobile.
Here are the development procedure and tips.
1. Mobile devices are 1/20 the power of PC. If it runs great on PC there is no evidence the game will run great on mobile.
2. If your game is going mobile. Your primary test device is mobile. Keep your mobile device hooked up to your computer. Develop a quick way to test on your device. And test on that. It's fine to test on the PC more often, but make sure that 1/4 tests are done on the mobile device.
3. There are tutorials for both memory and performance tips.
4. If you can. Keep your custom all the time update logic to 24-30FPS. You can do this by a EveryTick 0.0033.
5. Batch common layer graphics into 1 or few Sprite Objects(ie all types of weapon fire in just BulletsSprite, All HUD elements in HUDSprite)
6. I've mentioned this before. But it always bares repeating. Minimize your use of Plugins. Some Plugins have heavy overhead on mobile devices. I will give a sample. However these samples are device dependent. Newer devices handle more at one time.
RotatePlugin. Graphic size made no difference. 20FPS on a 100x100 sprite, used 50% of the CPU
EveryTick 0.0033. Set Angle + 8. Graphic size 2048x2048. 60FPS, used 15% of the CPU
PIN Behavour(not actually pinned to anything, just added to the object)
No Pins. 220 objects, 30fps
With Pins. 60 objects 30fps
*** so with pins, that don't do anything the game performance was cut in less than half.
MoveTo(third party plugin)
MoveTo, moving. 20FPS, 60% cpu usage.
So I'm going to assume you
Assumed PC and Mobile are close enough to the same power
Didn't test regularly on mobile
May have looked at performance tips
Didn't consider logic FPS(really I only do this)
Didn't batch your graphics into layered objects(most new users make 1 visual to 1 Sprite... kills performance)
Probably overloaded your game with lots of behaviours
1. Disable EVERYTHING and only enable 1 Layout(i suggest your simplest layout to start)
2. Test your loader Layout on mobile.
3. If it's slow. Go through your objects by disabling them until you hit 50+fps
4. Re-enable until you find what slows down your game.
5. Find a performance solution or ask the forums for a solution.
6. If the problem is Fixed go to 7. If it's still slow go back to 4.
7. Your Layout is running smooth. Go to next simplest Layout.
8. Good luck