Your answer is too simplistic; how can you assure reducing the graphics may completely solve the issue, when most of the people here can't even get past the loading screen? If it were for so, nobody would have complained.
Even though the question has been answered, I recommend that users having this issue should try reducing their 'resolution' setting in Graphics. It makes your screen quality potato mode but reduces lag. I use an iPad 3 and I reduced my resolution and the problem's solved. The developers really went on-board with the new Unity
And to back up my theory, I have tested Tanktastic 2.0 on all my potato and budget devices, half of them can't open up the game and the other half struggles to get above 18 FPS at high settings. The Frames Per Second difference when having high settings and low settings is almost non-existent, as GHOR hasn't added additional adjustment for the user which are very critical. Instead of being specific, the settings are too simplistic, which makes it very frustrating to find which is the main cause behind the FPS drop. Not to keep on count most of the devices from 2013 and back aren't capable of running TT not even at low settings.
As far as the story goes, I've discovered that the reason why people encounter FPS drops may be because the shooting after-effects causes the FPS to go from 30 to 5 and slowly comes back to 25 FPS. It is advised that people running mid-end devices keep the special effects at medium or low, as high requires an intensive amount of RAM usage and a pretty powerful processor. Another theory might be that the Shadow setting is always on, even when you have deactivated it.