I made a new animation texture and initially stacked the 4 frames one above the other and used

llSetTextureAnim(ANIM_ON | LOOP, ALL_SIDES, 1, 4, 0, 0, 1.5);

without success. Tried it in SL and it worked fine. I had to change my texture into a 2x2 grid and use

llSetTextureAnim(ANIM_ON | LOOP, ALL_SIDES, 2, 2, 0, 0, 1.5);

Now it works.