Model with a small amount of polygons causes lags

I have no idea where you got your number 450 from. Here are only the first model stats:

 // PartName        Verts   Tris    submesh  Count  T_Vert  T_Tris
 // -------------------------------------------------------------
 // Bus Body        1068    921        7      x1    1068    921
 // Door             152    268        4      x4     608    1072
 // Wheel            130    150        2      x4     520    600
 // Lower Body       130     80        2      x1     130    80
 // Wheel cover       36     20        2      x4     144    80
 // connector         96     52        1      x1      96    52
 // driverwindow      88    132        3      x1      88    132
 // SideWindow        96    148        3      x9     864    1332
 // BrakeLight        40     20        2      x4     160    80
 // ---------------------------------------------------------------
 //                                                 3678    4349

Since all materials by default uses the Standard shader you get several batches for each part due to lights, shadows, ... The whole model issues 102 batches with the standard shader. The vertex count of each subpart is too high for dynamical batching. The model uses 11 materials. When the model is statically batched we get 44 batches (4 x 11). Though static batching is only an option if the model does not move and have no moving parts.

To sum up: This is a very bad model for a game. It uses not a single texture but only solid color materials. The optimal case would be two materials (1 opaque, 1 transparent) and each with a single texture. Though this model has way too much detail in the geometry which could have been drawn on the texture / normalmap. Only the 9 side windows have 864 vertices and 1332 triangles which is more than the whole body. The wheels also have way too much geometric detail.

When a texture would have been used a single wheel (with 12 steps) would only need 48 vertices and 44 triangles. Also if the poly count becomes a problem the inner face of the wheel could be cut out (which would mean -10 triangles -12 vertices)

This is a very bad model for use on mobile devices.