You need heat sinks and force air (fan) cooling if you want to run the motors at 1.5A with quality A4988 drivers. With Chinese drivers, I don't think that I would go that high with the current.
This Pololu page for the A4988 has the procedure for adjusting the coil current. You must be careful to use the right value for the sense resistors in the formula to calculate the Vref to be set. The Pololu page shows how to identify the resistors. Pololu boards use 0.05Ω or 0.068Ω resistors. Chinese boards can use different values. Some of mine use 0.100Ω (marked R100).