The to battery were replaced by a 15 V battery, would the current through the 70 ohm resistor increase se or remain the same

Since you didn’t state the other voltage you’re working with, I’ll tell you how to determine if it’s larger or smaller. Ohm’s law is V = I*R, where V is the voltage, I is the current, and R is the resistance. Since R is constant, increasing V will increase I and vice versa.

If the other battery has a voltage larger than 15 V, then the current will increase. If it is lower than 15 V, the current will decrease. If the voltage is the same, then the current will be also.

Hope this helps!