The number of turns of the coil of a moving coil galvanometer is...

Current sensitivity = Voltage sensitivity $\times R$

If current sensitivity is made $1 . 5$ times, then $R$ also increase $1 . 5$ times.

Hence, voltage sensitivity $= \dfrac{1 . 5 \times \text{current sensitivity}}{1 . 5 \times R}$

= no change.