How large are those tiles?
Do they all share the same textures?
How far from cam are they?
(reasons I ask are: too many surfaces make the rendering slower, too many surfaces near to the cam are especially worse and if each has its own textures it could simply be that it floods the bandwidth with transfering textures to graphic card and back all the time)
Do they all share the same textures?
How far from cam are they?
(reasons I ask are: too many surfaces make the rendering slower, too many surfaces near to the cam are especially worse and if each has its own textures it could simply be that it floods the bandwidth with transfering textures to graphic card and back all the time)