Doesn’t matter if its your own aircraft or not, the seats on C152 are only adjustable for and aft, a mechanic is not gonna change that. It is what it is. If you can’t see over the glareshield you need to sit on a pillow 
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That on the picture is an eye reference indicator found on bigger aircraft with seats adjustable in all axis and adjustable rudder pedal position. The eye position is the same for every pilot as you change seat position until the white ball is hidden behind the red ball from your seating position.
On those kind of aircraft its vitally important that you have the correct seating position and eye height to have the correct view out of the window and over the nose for CAT II / III operations for example.
On any other aircraft, like C152 there is no correct answer to the question whether eye-position is correct. It depends on the length of your legs as this determines seat position and you height.