Nice done this Model. I like it. But yes, You should do some “fixings” at the round Surfaces. The Rest is lowPoly enough i think.
Try this Trick:
Disable the Collision of all Faces of this Model.
Copy the Model an delete all unnecessary Faces, diesable Textures of the Rest and set them also to invisible and collision ON.
Now You have a lowest-Poly-Model just for Collision detection. Make it Parent to the visible Model like a Hull.
Such a Hull is easier to calculate with Physics and Stuff. That means, You can use more detailed Models inside.
Disabling the Collision of most Faces as possible saves a lot Power. And even more with using a “Collision Hull Mesh Object”. Try it, and You will see.
Our little GE has more Power than most People think. This is not only a Blender Trick. Some other Engines goes a similar Way. This is a regular Technique.