Varathane Spar Urethane Over Painted Wood

I painted cutout pieces for an outdoor sign I am making. I put a coat of primer and 2 coats of water based exterior paint on so far. I am planning to apply some Varathane Spar Urethane, clear water based for added protection. The can reccomends 4 coats, but thats on bare wood. Being that its painted, do I still need 4 coats or would like 2 work? Thanks