The Roadster 1.5 was actually the first production car, 1.0 refers to some very early cars with two speed gearbox that was replaced in service making even those early Roadsters 1.5.
The 1.5 original styling looked like this:
The interior still had the gear lever that was designed for the 2 speed gearbox.
The series 2 kept the same external styling and updated the interior with push buttons instead of the gear stick.
Around this time some significant changes were made to the Power Electronics Module (PEM) that communicates between the battery and motor and IIRC also handles battery management.
The 2.5 saw further refinement of the interior allowing for a double DIN music system to be installed
Note how they moved the vents to the top of the dash to allow for the double DIN.
At the same time Franz Von Holzhausen refreshed the external styling with more aerodynamic openings.
Almost all 1.5's were non sports except for a few prototypes.
The sport model has a hand wound motor and modified PEM plus adjustable suspension.
I think the largest number made were 2.0's and they feature the newer PEM, loose the silly gear stick but retain the original styling.