Lakes:
Soild state relays have no contacts to wear out due to arcing when switching an inductive load like a motor.
But SSR relays can have much difficulty switching high inductive loads such as large motors unless you equip them with a properly size snubber circuit. SSRs work much better with pure resistive loads. Also if actually running at 15 to 20amps they require a very large heat sink to keep from destroying the SSR. Most SSRs have about a 2 volt drop across them and at 20 amps that is 40 watts of heat that needs to be removed from the package. Actually at the 15-20 amp range you should be looking at 'motor controllers', which are large multi-pole electromagnetic relays designed to turn motors on remotely. They often contain built in 'overloads' and/or fuses.
15 to 20amps of AC current powering a motor is not something to fool around with unless you have the proper knowledge and experiences working at such power levels.
Lefty