AC motor control with triac or relay
It is not a good idea to control a motor using either electromechanical or solid-state relays that are not rated for motor control. Equipment that is so rated usually have a rating plate or catalog listing that indicates motor power rating in either horsepower or kW along with the related voltage and number of phases. Some manufacturers may have more compact equipment than others for a particular power rating. One reason for that is that the same basic design may be used for a range of motor power ratings. One manufacture may use a single design for 3.5, 5 and 7.5 Hp. While another may have a design for 1.5, 2 and 3.5 Hp. It pays to put some effort into shopping.

One 1.5 Hp rated relay per phase is not a substitute for a properly rated 3-phase contactor. You can probably use either a 2-pole relay or a 1-pole relay for a single-phase motor, but not two relays with lower ratings.