Just because there is deck space doesn't mean these ships are suitable platforms. You also need to be able to detect targets to target your missiles. And have self-defence capability. A helicopter like Z-9EC could perform ASW but if the base vessel is not sonar equiped the heli must have a dipping sonar and/or ability to launch ASW buoys and process signal from them. Platform must also be able to refuel and rearm and maintain the heli. Z-9EC has a low frequency dipping sonar and can carry light ASW torpedoes.
Where on deck would you place those AShM? Where is the helicopter hangar and support facility?
As for the 1500 ton ship, depends on whether it is Type 056 based or e.g. Haixun class cutter. Here too, the question is where the missiles would go + self defence.
056 Coast Guard OPV
Haixun class MSA cutter